1menu "printk and dmesg options" 2 3config PRINTK_TIME 4 bool "Show timing information on printks" 5 depends on PRINTK 6 help 7 Selecting this option causes time stamps of the printk() 8 messages to be added to the output of the syslog() system 9 call and at the console. 10 11 The timestamp is always recorded internally, and exported 12 to /dev/kmsg. This flag just specifies if the timestamp should 13 be included, not that the timestamp is recorded. 14 15 The behavior is also controlled by the kernel command line 16 parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst 17 18config CONSOLE_LOGLEVEL_DEFAULT 19 int "Default console loglevel (1-15)" 20 range 1 15 21 default "7" 22 help 23 Default loglevel to determine what will be printed on the console. 24 25 Setting a default here is equivalent to passing in loglevel=<x> in 26 the kernel bootargs. loglevel=<x> continues to override whatever 27 value is specified here as well. 28 29 Note: This does not affect the log level of un-prefixed printk() 30 usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT 31 option. 32 33config MESSAGE_LOGLEVEL_DEFAULT 34 int "Default message log level (1-7)" 35 range 1 7 36 default "4" 37 help 38 Default log level for printk statements with no specified priority. 39 40 This was hard-coded to KERN_WARNING since at least 2.6.10 but folks 41 that are auditing their logs closely may want to set it to a lower 42 priority. 43 44 Note: This does not affect what message level gets printed on the console 45 by default. To change that, use loglevel=<x> in the kernel bootargs, 46 or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value. 47 48config BOOT_PRINTK_DELAY 49 bool "Delay each boot printk message by N milliseconds" 50 depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY 51 help 52 This build option allows you to read kernel boot messages 53 by inserting a short delay after each one. The delay is 54 specified in milliseconds on the kernel command line, 55 using "boot_delay=N". 56 57 It is likely that you would also need to use "lpj=M" to preset 58 the "loops per jiffie" value. 59 See a previous boot log for the "lpj" value to use for your 60 system, and then set "lpj=M" before setting "boot_delay=N". 61 NOTE: Using this option may adversely affect SMP systems. 62 I.e., processors other than the first one may not boot up. 63 BOOT_PRINTK_DELAY also may cause LOCKUP_DETECTOR to detect 64 what it believes to be lockup conditions. 65 66config DYNAMIC_DEBUG 67 bool "Enable dynamic printk() support" 68 default n 69 depends on PRINTK 70 depends on DEBUG_FS 71 help 72 73 Compiles debug level messages into the kernel, which would not 74 otherwise be available at runtime. These messages can then be 75 enabled/disabled based on various levels of scope - per source file, 76 function, module, format string, and line number. This mechanism 77 implicitly compiles in all pr_debug() and dev_dbg() calls, which 78 enlarges the kernel text size by about 2%. 79 80 If a source file is compiled with DEBUG flag set, any 81 pr_debug() calls in it are enabled by default, but can be 82 disabled at runtime as below. Note that DEBUG flag is 83 turned on by many CONFIG_*DEBUG* options. 84 85 Usage: 86 87 Dynamic debugging is controlled via the 'dynamic_debug/control' file, 88 which is contained in the 'debugfs' filesystem. Thus, the debugfs 89 filesystem must first be mounted before making use of this feature. 90 We refer the control file as: <debugfs>/dynamic_debug/control. This 91 file contains a list of the debug statements that can be enabled. The 92 format for each line of the file is: 93 94 filename:lineno [module]function flags format 95 96 filename : source file of the debug statement 97 lineno : line number of the debug statement 98 module : module that contains the debug statement 99 function : function that contains the debug statement 100 flags : '=p' means the line is turned 'on' for printing 101 format : the format used for the debug statement 102 103 From a live system: 104 105 nullarbor:~ # cat <debugfs>/dynamic_debug/control 106 # filename:lineno [module]function flags format 107 fs/aio.c:222 [aio]__put_ioctx =_ "__put_ioctx:\040freeing\040%p\012" 108 fs/aio.c:248 [aio]ioctx_alloc =_ "ENOMEM:\040nr_events\040too\040high\012" 109 fs/aio.c:1770 [aio]sys_io_cancel =_ "calling\040cancel\012" 110 111 Example usage: 112 113 // enable the message at line 1603 of file svcsock.c 114 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 115 <debugfs>/dynamic_debug/control 116 117 // enable all the messages in file svcsock.c 118 nullarbor:~ # echo -n 'file svcsock.c +p' > 119 <debugfs>/dynamic_debug/control 120 121 // enable all the messages in the NFS server module 122 nullarbor:~ # echo -n 'module nfsd +p' > 123 <debugfs>/dynamic_debug/control 124 125 // enable all 12 messages in the function svc_process() 126 nullarbor:~ # echo -n 'func svc_process +p' > 127 <debugfs>/dynamic_debug/control 128 129 // disable all 12 messages in the function svc_process() 130 nullarbor:~ # echo -n 'func svc_process -p' > 131 <debugfs>/dynamic_debug/control 132 133 See Documentation/admin-guide/dynamic-debug-howto.rst for additional 134 information. 135 136endmenu # "printk and dmesg options" 137 138menu "Compile-time checks and compiler options" 139 140config DEBUG_INFO 141 bool "Compile the kernel with debug info" 142 depends on DEBUG_KERNEL && !COMPILE_TEST 143 help 144 If you say Y here the resulting kernel image will include 145 debugging info resulting in a larger kernel image. 146 This adds debug symbols to the kernel and modules (gcc -g), and 147 is needed if you intend to use kernel crashdump or binary object 148 tools like crash, kgdb, LKCD, gdb, etc on the kernel. 149 Say Y here only if you plan to debug the kernel. 150 151 If unsure, say N. 152 153config DEBUG_INFO_REDUCED 154 bool "Reduce debugging information" 155 depends on DEBUG_INFO 156 help 157 If you say Y here gcc is instructed to generate less debugging 158 information for structure types. This means that tools that 159 need full debugging information (like kgdb or systemtap) won't 160 be happy. But if you merely need debugging information to 161 resolve line numbers there is no loss. Advantage is that 162 build directory object sizes shrink dramatically over a full 163 DEBUG_INFO build and compile times are reduced too. 164 Only works with newer gcc versions. 165 166config DEBUG_INFO_SPLIT 167 bool "Produce split debuginfo in .dwo files" 168 depends on DEBUG_INFO && !FRV 169 help 170 Generate debug info into separate .dwo files. This significantly 171 reduces the build directory size for builds with DEBUG_INFO, 172 because it stores the information only once on disk in .dwo 173 files instead of multiple times in object files and executables. 174 In addition the debug information is also compressed. 175 176 Requires recent gcc (4.7+) and recent gdb/binutils. 177 Any tool that packages or reads debug information would need 178 to know about the .dwo files and include them. 179 Incompatible with older versions of ccache. 180 181config DEBUG_INFO_DWARF4 182 bool "Generate dwarf4 debuginfo" 183 depends on DEBUG_INFO 184 help 185 Generate dwarf4 debug info. This requires recent versions 186 of gcc and gdb. It makes the debug information larger. 187 But it significantly improves the success of resolving 188 variables in gdb on optimized code. 189 190config GDB_SCRIPTS 191 bool "Provide GDB scripts for kernel debugging" 192 depends on DEBUG_INFO 193 help 194 This creates the required links to GDB helper scripts in the 195 build directory. If you load vmlinux into gdb, the helper 196 scripts will be automatically imported by gdb as well, and 197 additional functions are available to analyze a Linux kernel 198 instance. See Documentation/dev-tools/gdb-kernel-debugging.rst 199 for further details. 200 201config ENABLE_WARN_DEPRECATED 202 bool "Enable __deprecated logic" 203 default y 204 help 205 Enable the __deprecated logic in the kernel build. 206 Disable this to suppress the "warning: 'foo' is deprecated 207 (declared at kernel/power/somefile.c:1234)" messages. 208 209config ENABLE_MUST_CHECK 210 bool "Enable __must_check logic" 211 default y 212 help 213 Enable the __must_check logic in the kernel build. Disable this to 214 suppress the "warning: ignoring return value of 'foo', declared with 215 attribute warn_unused_result" messages. 216 217config FRAME_WARN 218 int "Warn for stack frames larger than (needs gcc 4.4)" 219 range 0 8192 220 default 3072 if KASAN_EXTRA 221 default 2048 if GCC_PLUGIN_LATENT_ENTROPY 222 default 1280 if (!64BIT && PARISC) 223 default 1024 if (!64BIT && !PARISC) 224 default 2048 if 64BIT 225 help 226 Tell gcc to warn at build time for stack frames larger than this. 227 Setting this too low will cause a lot of warnings. 228 Setting it to 0 disables the warning. 229 Requires gcc 4.4 230 231config STRIP_ASM_SYMS 232 bool "Strip assembler-generated symbols during link" 233 default n 234 help 235 Strip internal assembler-generated symbols during a link (symbols 236 that look like '.Lxxx') so they don't pollute the output of 237 get_wchan() and suchlike. 238 239config READABLE_ASM 240 bool "Generate readable assembler code" 241 depends on DEBUG_KERNEL 242 help 243 Disable some compiler optimizations that tend to generate human unreadable 244 assembler output. This may make the kernel slightly slower, but it helps 245 to keep kernel developers who have to stare a lot at assembler listings 246 sane. 247 248config UNUSED_SYMBOLS 249 bool "Enable unused/obsolete exported symbols" 250 default y if X86 251 help 252 Unused but exported symbols make the kernel needlessly bigger. For 253 that reason most of these unused exports will soon be removed. This 254 option is provided temporarily to provide a transition period in case 255 some external kernel module needs one of these symbols anyway. If you 256 encounter such a case in your module, consider if you are actually 257 using the right API. (rationale: since nobody in the kernel is using 258 this in a module, there is a pretty good chance it's actually the 259 wrong interface to use). If you really need the symbol, please send a 260 mail to the linux kernel mailing list mentioning the symbol and why 261 you really need it, and what the merge plan to the mainline kernel for 262 your module is. 263 264config PAGE_OWNER 265 bool "Track page owner" 266 depends on DEBUG_KERNEL && STACKTRACE_SUPPORT 267 select DEBUG_FS 268 select STACKTRACE 269 select STACKDEPOT 270 select PAGE_EXTENSION 271 help 272 This keeps track of what call chain is the owner of a page, may 273 help to find bare alloc_page(s) leaks. Even if you include this 274 feature on your build, it is disabled in default. You should pass 275 "page_owner=on" to boot parameter in order to enable it. Eats 276 a fair amount of memory if enabled. See tools/vm/page_owner_sort.c 277 for user-space helper. 278 279 If unsure, say N. 280 281config DEBUG_FS 282 bool "Debug Filesystem" 283 help 284 debugfs is a virtual file system that kernel developers use to put 285 debugging files into. Enable this option to be able to read and 286 write to these files. 287 288 For detailed documentation on the debugfs API, see 289 Documentation/filesystems/. 290 291 If unsure, say N. 292 293config HEADERS_CHECK 294 bool "Run 'make headers_check' when building vmlinux" 295 depends on !UML 296 help 297 This option will extract the user-visible kernel headers whenever 298 building the kernel, and will run basic sanity checks on them to 299 ensure that exported files do not attempt to include files which 300 were not exported, etc. 301 302 If you're making modifications to header files which are 303 relevant for userspace, say 'Y', and check the headers 304 exported to $(INSTALL_HDR_PATH) (usually 'usr/include' in 305 your build tree), to make sure they're suitable. 306 307config DEBUG_SECTION_MISMATCH 308 bool "Enable full Section mismatch analysis" 309 help 310 The section mismatch analysis checks if there are illegal 311 references from one section to another section. 312 During linktime or runtime, some sections are dropped; 313 any use of code/data previously in these sections would 314 most likely result in an oops. 315 In the code, functions and variables are annotated with 316 __init,, etc. (see the full list in include/linux/init.h), 317 which results in the code/data being placed in specific sections. 318 The section mismatch analysis is always performed after a full 319 kernel build, and enabling this option causes the following 320 additional steps to occur: 321 - Add the option -fno-inline-functions-called-once to gcc commands. 322 When inlining a function annotated with __init in a non-init 323 function, we would lose the section information and thus 324 the analysis would not catch the illegal reference. 325 This option tells gcc to inline less (but it does result in 326 a larger kernel). 327 - Run the section mismatch analysis for each module/built-in.o file. 328 When we run the section mismatch analysis on vmlinux.o, we 329 lose valuable information about where the mismatch was 330 introduced. 331 Running the analysis for each module/built-in.o file 332 tells where the mismatch happens much closer to the 333 source. The drawback is that the same mismatch is 334 reported at least twice. 335 - Enable verbose reporting from modpost in order to help resolve 336 the section mismatches that are reported. 337 338config SECTION_MISMATCH_WARN_ONLY 339 bool "Make section mismatch errors non-fatal" 340 default y 341 help 342 If you say N here, the build process will fail if there are any 343 section mismatch, instead of just throwing warnings. 344 345 If unsure, say Y. 346 347# 348# Select this config option from the architecture Kconfig, if it 349# is preferred to always offer frame pointers as a config 350# option on the architecture (regardless of KERNEL_DEBUG): 351# 352config ARCH_WANT_FRAME_POINTERS 353 bool 354 355config FRAME_POINTER 356 bool "Compile the kernel with frame pointers" 357 depends on DEBUG_KERNEL && \ 358 (CRIS || M68K || FRV || UML || \ 359 SUPERH || BLACKFIN || MN10300 || METAG) || \ 360 ARCH_WANT_FRAME_POINTERS 361 default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS 362 help 363 If you say Y here the resulting kernel image will be slightly 364 larger and slower, but it gives very useful debugging information 365 in case of kernel bugs. (precise oopses/stacktraces/warnings) 366 367config STACK_VALIDATION 368 bool "Compile-time stack metadata validation" 369 depends on HAVE_STACK_VALIDATION 370 default n 371 help 372 Add compile-time checks to validate stack metadata, including frame 373 pointers (if CONFIG_FRAME_POINTER is enabled). This helps ensure 374 that runtime stack traces are more reliable. 375 376 This is also a prerequisite for generation of ORC unwind data, which 377 is needed for CONFIG_UNWINDER_ORC. 378 379 For more information, see 380 tools/objtool/Documentation/stack-validation.txt. 381 382config DEBUG_FORCE_WEAK_PER_CPU 383 bool "Force weak per-cpu definitions" 384 depends on DEBUG_KERNEL 385 help 386 s390 and alpha require percpu variables in modules to be 387 defined weak to work around addressing range issue which 388 puts the following two restrictions on percpu variable 389 definitions. 390 391 1. percpu symbols must be unique whether static or not 392 2. percpu variables can't be defined inside a function 393 394 To ensure that generic code follows the above rules, this 395 option forces all percpu variables to be defined as weak. 396 397endmenu # "Compiler options" 398 399config MAGIC_SYSRQ 400 bool "Magic SysRq key" 401 depends on !UML 402 help 403 If you say Y here, you will have some control over the system even 404 if the system crashes for example during kernel debugging (e.g., you 405 will be able to flush the buffer cache to disk, reboot the system 406 immediately or dump some status information). This is accomplished 407 by pressing various keys while holding SysRq (Alt+PrintScreen). It 408 also works on a serial console (on PC hardware at least), if you 409 send a BREAK and then within 5 seconds a command keypress. The 410 keys are documented in <file:Documentation/admin-guide/sysrq.rst>. 411 Don't say Y unless you really know what this hack does. 412 413config MAGIC_SYSRQ_DEFAULT_ENABLE 414 hex "Enable magic SysRq key functions by default" 415 depends on MAGIC_SYSRQ 416 default 0x1 417 help 418 Specifies which SysRq key functions are enabled by default. 419 This may be set to 1 or 0 to enable or disable them all, or 420 to a bitmask as described in Documentation/admin-guide/sysrq.rst. 421 422config MAGIC_SYSRQ_SERIAL 423 bool "Enable magic SysRq key over serial" 424 depends on MAGIC_SYSRQ 425 default y 426 help 427 Many embedded boards have a disconnected TTL level serial which can 428 generate some garbage that can lead to spurious false sysrq detects. 429 This option allows you to decide whether you want to enable the 430 magic SysRq key. 431 432config DEBUG_KERNEL 433 bool "Kernel debugging" 434 help 435 Say Y here if you are developing drivers or trying to debug and 436 identify kernel problems. 437 438menu "Memory Debugging" 439 440source mm/Kconfig.debug 441 442config DEBUG_OBJECTS 443 bool "Debug object operations" 444 depends on DEBUG_KERNEL 445 help 446 If you say Y here, additional code will be inserted into the 447 kernel to track the life time of various objects and validate 448 the operations on those objects. 449 450config DEBUG_OBJECTS_SELFTEST 451 bool "Debug objects selftest" 452 depends on DEBUG_OBJECTS 453 help 454 This enables the selftest of the object debug code. 455 456config DEBUG_OBJECTS_FREE 457 bool "Debug objects in freed memory" 458 depends on DEBUG_OBJECTS 459 help 460 This enables checks whether a k/v free operation frees an area 461 which contains an object which has not been deactivated 462 properly. This can make kmalloc/kfree-intensive workloads 463 much slower. 464 465config DEBUG_OBJECTS_TIMERS 466 bool "Debug timer objects" 467 depends on DEBUG_OBJECTS 468 help 469 If you say Y here, additional code will be inserted into the 470 timer routines to track the life time of timer objects and 471 validate the timer operations. 472 473config DEBUG_OBJECTS_WORK 474 bool "Debug work objects" 475 depends on DEBUG_OBJECTS 476 help 477 If you say Y here, additional code will be inserted into the 478 work queue routines to track the life time of work objects and 479 validate the work operations. 480 481config DEBUG_OBJECTS_RCU_HEAD 482 bool "Debug RCU callbacks objects" 483 depends on DEBUG_OBJECTS 484 help 485 Enable this to turn on debugging of RCU list heads (call_rcu() usage). 486 487config DEBUG_OBJECTS_PERCPU_COUNTER 488 bool "Debug percpu counter objects" 489 depends on DEBUG_OBJECTS 490 help 491 If you say Y here, additional code will be inserted into the 492 percpu counter routines to track the life time of percpu counter 493 objects and validate the percpu counter operations. 494 495config DEBUG_OBJECTS_ENABLE_DEFAULT 496 int "debug_objects bootup default value (0-1)" 497 range 0 1 498 default "1" 499 depends on DEBUG_OBJECTS 500 help 501 Debug objects boot parameter default value 502 503config DEBUG_SLAB 504 bool "Debug slab memory allocations" 505 depends on DEBUG_KERNEL && SLAB 506 help 507 Say Y here to have the kernel do limited verification on memory 508 allocation as well as poisoning memory on free to catch use of freed 509 memory. This can make kmalloc/kfree-intensive workloads much slower. 510 511config DEBUG_SLAB_LEAK 512 bool "Memory leak debugging" 513 depends on DEBUG_SLAB 514 515config SLUB_DEBUG_ON 516 bool "SLUB debugging on by default" 517 depends on SLUB && SLUB_DEBUG 518 default n 519 help 520 Boot with debugging on by default. SLUB boots by default with 521 the runtime debug capabilities switched off. Enabling this is 522 equivalent to specifying the "slub_debug" parameter on boot. 523 There is no support for more fine grained debug control like 524 possible with slub_debug=xxx. SLUB debugging may be switched 525 off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying 526 "slub_debug=-". 527 528config SLUB_STATS 529 default n 530 bool "Enable SLUB performance statistics" 531 depends on SLUB && SYSFS 532 help 533 SLUB statistics are useful to debug SLUBs allocation behavior in 534 order find ways to optimize the allocator. This should never be 535 enabled for production use since keeping statistics slows down 536 the allocator by a few percentage points. The slabinfo command 537 supports the determination of the most active slabs to figure 538 out which slabs are relevant to a particular load. 539 Try running: slabinfo -DA 540 541config HAVE_DEBUG_KMEMLEAK 542 bool 543 544config DEBUG_KMEMLEAK 545 bool "Kernel memory leak detector" 546 depends on DEBUG_KERNEL && HAVE_DEBUG_KMEMLEAK 547 select DEBUG_FS 548 select STACKTRACE if STACKTRACE_SUPPORT 549 select KALLSYMS 550 select CRC32 551 help 552 Say Y here if you want to enable the memory leak 553 detector. The memory allocation/freeing is traced in a way 554 similar to the Boehm's conservative garbage collector, the 555 difference being that the orphan objects are not freed but 556 only shown in /sys/kernel/debug/kmemleak. Enabling this 557 feature will introduce an overhead to memory 558 allocations. See Documentation/dev-tools/kmemleak.rst for more 559 details. 560 561 Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances 562 of finding leaks due to the slab objects poisoning. 563 564 In order to access the kmemleak file, debugfs needs to be 565 mounted (usually at /sys/kernel/debug). 566 567config DEBUG_KMEMLEAK_EARLY_LOG_SIZE 568 int "Maximum kmemleak early log entries" 569 depends on DEBUG_KMEMLEAK 570 range 200 40000 571 default 400 572 help 573 Kmemleak must track all the memory allocations to avoid 574 reporting false positives. Since memory may be allocated or 575 freed before kmemleak is initialised, an early log buffer is 576 used to store these actions. If kmemleak reports "early log 577 buffer exceeded", please increase this value. 578 579config DEBUG_KMEMLEAK_TEST 580 tristate "Simple test for the kernel memory leak detector" 581 depends on DEBUG_KMEMLEAK && m 582 help 583 This option enables a module that explicitly leaks memory. 584 585 If unsure, say N. 586 587config DEBUG_KMEMLEAK_DEFAULT_OFF 588 bool "Default kmemleak to off" 589 depends on DEBUG_KMEMLEAK 590 help 591 Say Y here to disable kmemleak by default. It can then be enabled 592 on the command line via kmemleak=on. 593 594config DEBUG_STACK_USAGE 595 bool "Stack utilization instrumentation" 596 depends on DEBUG_KERNEL && !IA64 597 help 598 Enables the display of the minimum amount of free stack which each 599 task has ever had available in the sysrq-T and sysrq-P debug output. 600 601 This option will slow down process creation somewhat. 602 603config DEBUG_VM 604 bool "Debug VM" 605 depends on DEBUG_KERNEL 606 help 607 Enable this to turn on extended checks in the virtual-memory system 608 that may impact performance. 609 610 If unsure, say N. 611 612config DEBUG_VM_VMACACHE 613 bool "Debug VMA caching" 614 depends on DEBUG_VM 615 help 616 Enable this to turn on VMA caching debug information. Doing so 617 can cause significant overhead, so only enable it in non-production 618 environments. 619 620 If unsure, say N. 621 622config DEBUG_VM_RB 623 bool "Debug VM red-black trees" 624 depends on DEBUG_VM 625 help 626 Enable VM red-black tree debugging information and extra validations. 627 628 If unsure, say N. 629 630config DEBUG_VM_PGFLAGS 631 bool "Debug page-flags operations" 632 depends on DEBUG_VM 633 help 634 Enables extra validation on page flags operations. 635 636 If unsure, say N. 637 638config ARCH_HAS_DEBUG_VIRTUAL 639 bool 640 641config DEBUG_VIRTUAL 642 bool "Debug VM translations" 643 depends on DEBUG_KERNEL && ARCH_HAS_DEBUG_VIRTUAL 644 help 645 Enable some costly sanity checks in virtual to page code. This can 646 catch mistakes with virt_to_page() and friends. 647 648 If unsure, say N. 649 650config DEBUG_NOMMU_REGIONS 651 bool "Debug the global anon/private NOMMU mapping region tree" 652 depends on DEBUG_KERNEL && !MMU 653 help 654 This option causes the global tree of anonymous and private mapping 655 regions to be regularly checked for invalid topology. 656 657config DEBUG_MEMORY_INIT 658 bool "Debug memory initialisation" if EXPERT 659 default !EXPERT 660 help 661 Enable this for additional checks during memory initialisation. 662 The sanity checks verify aspects of the VM such as the memory model 663 and other information provided by the architecture. Verbose 664 information will be printed at KERN_DEBUG loglevel depending 665 on the mminit_loglevel= command-line option. 666 667 If unsure, say Y 668 669config MEMORY_NOTIFIER_ERROR_INJECT 670 tristate "Memory hotplug notifier error injection module" 671 depends on MEMORY_HOTPLUG_SPARSE && NOTIFIER_ERROR_INJECTION 672 help 673 This option provides the ability to inject artificial errors to 674 memory hotplug notifier chain callbacks. It is controlled through 675 debugfs interface under /sys/kernel/debug/notifier-error-inject/memory 676 677 If the notifier call chain should be failed with some events 678 notified, write the error code to "actions/<notifier event>/error". 679 680 Example: Inject memory hotplug offline error (-12 == -ENOMEM) 681 682 # cd /sys/kernel/debug/notifier-error-inject/memory 683 # echo -12 > actions/MEM_GOING_OFFLINE/error 684 # echo offline > /sys/devices/system/memory/memoryXXX/state 685 bash: echo: write error: Cannot allocate memory 686 687 To compile this code as a module, choose M here: the module will 688 be called memory-notifier-error-inject. 689 690 If unsure, say N. 691 692config DEBUG_PER_CPU_MAPS 693 bool "Debug access to per_cpu maps" 694 depends on DEBUG_KERNEL 695 depends on SMP 696 help 697 Say Y to verify that the per_cpu map being accessed has 698 been set up. This adds a fair amount of code to kernel memory 699 and decreases performance. 700 701 Say N if unsure. 702 703config DEBUG_HIGHMEM 704 bool "Highmem debugging" 705 depends on DEBUG_KERNEL && HIGHMEM 706 help 707 This option enables additional error checking for high memory 708 systems. Disable for production systems. 709 710config HAVE_DEBUG_STACKOVERFLOW 711 bool 712 713config DEBUG_STACKOVERFLOW 714 bool "Check for stack overflows" 715 depends on DEBUG_KERNEL && HAVE_DEBUG_STACKOVERFLOW 716 ---help--- 717 Say Y here if you want to check for overflows of kernel, IRQ 718 and exception stacks (if your architecture uses them). This 719 option will show detailed messages if free stack space drops 720 below a certain limit. 721 722 These kinds of bugs usually occur when call-chains in the 723 kernel get too deep, especially when interrupts are 724 involved. 725 726 Use this in cases where you see apparently random memory 727 corruption, especially if it appears in 'struct thread_info' 728 729 If in doubt, say "N". 730 731source "lib/Kconfig.kasan" 732 733endmenu # "Memory Debugging" 734 735config ARCH_HAS_KCOV 736 bool 737 help 738 KCOV does not have any arch-specific code, but currently it is enabled 739 only for x86_64. KCOV requires testing on other archs, and most likely 740 disabling of instrumentation for some early boot code. 741 742config KCOV 743 bool "Code coverage for fuzzing" 744 depends on ARCH_HAS_KCOV 745 select DEBUG_FS 746 select GCC_PLUGINS if !COMPILE_TEST 747 select GCC_PLUGIN_SANCOV if !COMPILE_TEST 748 help 749 KCOV exposes kernel code coverage information in a form suitable 750 for coverage-guided fuzzing (randomized testing). 751 752 If RANDOMIZE_BASE is enabled, PC values will not be stable across 753 different machines and across reboots. If you need stable PC values, 754 disable RANDOMIZE_BASE. 755 756 For more details, see Documentation/dev-tools/kcov.rst. 757 758config KCOV_ENABLE_COMPARISONS 759 bool "Enable comparison operands collection by KCOV" 760 depends on KCOV 761 default n 762 help 763 KCOV also exposes operands of every comparison in the instrumented 764 code along with operand sizes and PCs of the comparison instructions. 765 These operands can be used by fuzzing engines to improve the quality 766 of fuzzing coverage. 767 768config KCOV_INSTRUMENT_ALL 769 bool "Instrument all code by default" 770 depends on KCOV 771 default y if KCOV 772 help 773 If you are doing generic system call fuzzing (like e.g. syzkaller), 774 then you will want to instrument the whole kernel and you should 775 say y here. If you are doing more targeted fuzzing (like e.g. 776 filesystem fuzzing with AFL) then you will want to enable coverage 777 for more specific subsets of files, and should say n here. 778 779config DEBUG_SHIRQ 780 bool "Debug shared IRQ handlers" 781 depends on DEBUG_KERNEL 782 help 783 Enable this to generate a spurious interrupt as soon as a shared 784 interrupt handler is registered, and just before one is deregistered. 785 Drivers ought to be able to handle interrupts coming in at those 786 points; some don't and need to be caught. 787 788menu "Debug Lockups and Hangs" 789 790config LOCKUP_DETECTOR 791 bool 792 793config SOFTLOCKUP_DETECTOR 794 bool "Detect Soft Lockups" 795 depends on DEBUG_KERNEL && !S390 796 select LOCKUP_DETECTOR 797 help 798 Say Y here to enable the kernel to act as a watchdog to detect 799 soft lockups. 800 801 Softlockups are bugs that cause the kernel to loop in kernel 802 mode for more than 20 seconds, without giving other tasks a 803 chance to run. The current stack trace is displayed upon 804 detection and the system will stay locked up. 805 806config HARDLOCKUP_DETECTOR_PERF 807 bool 808 select SOFTLOCKUP_DETECTOR 809 810# 811# Enables a timestamp based low pass filter to compensate for perf based 812# hard lockup detection which runs too fast due to turbo modes. 813# 814config HARDLOCKUP_CHECK_TIMESTAMP 815 bool 816 817# 818# arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard 819# lockup detector rather than the perf based detector. 820# 821config HARDLOCKUP_DETECTOR 822 bool "Detect Hard Lockups" 823 depends on DEBUG_KERNEL && !S390 824 depends on HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_ARCH 825 select LOCKUP_DETECTOR 826 select HARDLOCKUP_DETECTOR_PERF if HAVE_HARDLOCKUP_DETECTOR_PERF 827 select HARDLOCKUP_DETECTOR_ARCH if HAVE_HARDLOCKUP_DETECTOR_ARCH 828 help 829 Say Y here to enable the kernel to act as a watchdog to detect 830 hard lockups. 831 832 Hardlockups are bugs that cause the CPU to loop in kernel mode 833 for more than 10 seconds, without letting other interrupts have a 834 chance to run. The current stack trace is displayed upon detection 835 and the system will stay locked up. 836 837config BOOTPARAM_HARDLOCKUP_PANIC 838 bool "Panic (Reboot) On Hard Lockups" 839 depends on HARDLOCKUP_DETECTOR 840 help 841 Say Y here to enable the kernel to panic on "hard lockups", 842 which are bugs that cause the kernel to loop in kernel 843 mode with interrupts disabled for more than 10 seconds (configurable 844 using the watchdog_thresh sysctl). 845 846 Say N if unsure. 847 848config BOOTPARAM_HARDLOCKUP_PANIC_VALUE 849 int 850 depends on HARDLOCKUP_DETECTOR 851 range 0 1 852 default 0 if !BOOTPARAM_HARDLOCKUP_PANIC 853 default 1 if BOOTPARAM_HARDLOCKUP_PANIC 854 855config BOOTPARAM_SOFTLOCKUP_PANIC 856 bool "Panic (Reboot) On Soft Lockups" 857 depends on SOFTLOCKUP_DETECTOR 858 help 859 Say Y here to enable the kernel to panic on "soft lockups", 860 which are bugs that cause the kernel to loop in kernel 861 mode for more than 20 seconds (configurable using the watchdog_thresh 862 sysctl), without giving other tasks a chance to run. 863 864 The panic can be used in combination with panic_timeout, 865 to cause the system to reboot automatically after a 866 lockup has been detected. This feature is useful for 867 high-availability systems that have uptime guarantees and 868 where a lockup must be resolved ASAP. 869 870 Say N if unsure. 871 872config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE 873 int 874 depends on SOFTLOCKUP_DETECTOR 875 range 0 1 876 default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC 877 default 1 if BOOTPARAM_SOFTLOCKUP_PANIC 878 879config DETECT_HUNG_TASK 880 bool "Detect Hung Tasks" 881 depends on DEBUG_KERNEL 882 default SOFTLOCKUP_DETECTOR 883 help 884 Say Y here to enable the kernel to detect "hung tasks", 885 which are bugs that cause the task to be stuck in 886 uninterruptible "D" state indefinitely. 887 888 When a hung task is detected, the kernel will print the 889 current stack trace (which you should report), but the 890 task will stay in uninterruptible state. If lockdep is 891 enabled then all held locks will also be reported. This 892 feature has negligible overhead. 893 894config DEFAULT_HUNG_TASK_TIMEOUT 895 int "Default timeout for hung task detection (in seconds)" 896 depends on DETECT_HUNG_TASK 897 default 120 898 help 899 This option controls the default timeout (in seconds) used 900 to determine when a task has become non-responsive and should 901 be considered hung. 902 903 It can be adjusted at runtime via the kernel.hung_task_timeout_secs 904 sysctl or by writing a value to 905 /proc/sys/kernel/hung_task_timeout_secs. 906 907 A timeout of 0 disables the check. The default is two minutes. 908 Keeping the default should be fine in most cases. 909 910config BOOTPARAM_HUNG_TASK_PANIC 911 bool "Panic (Reboot) On Hung Tasks" 912 depends on DETECT_HUNG_TASK 913 help 914 Say Y here to enable the kernel to panic on "hung tasks", 915 which are bugs that cause the kernel to leave a task stuck 916 in uninterruptible "D" state. 917 918 The panic can be used in combination with panic_timeout, 919 to cause the system to reboot automatically after a 920 hung task has been detected. This feature is useful for 921 high-availability systems that have uptime guarantees and 922 where a hung tasks must be resolved ASAP. 923 924 Say N if unsure. 925 926config BOOTPARAM_HUNG_TASK_PANIC_VALUE 927 int 928 depends on DETECT_HUNG_TASK 929 range 0 1 930 default 0 if !BOOTPARAM_HUNG_TASK_PANIC 931 default 1 if BOOTPARAM_HUNG_TASK_PANIC 932 933config WQ_WATCHDOG 934 bool "Detect Workqueue Stalls" 935 depends on DEBUG_KERNEL 936 help 937 Say Y here to enable stall detection on workqueues. If a 938 worker pool doesn't make forward progress on a pending work 939 item for over a given amount of time, 30s by default, a 940 warning message is printed along with dump of workqueue 941 state. This can be configured through kernel parameter 942 "workqueue.watchdog_thresh" and its sysfs counterpart. 943 944endmenu # "Debug lockups and hangs" 945 946config PANIC_ON_OOPS 947 bool "Panic on Oops" 948 help 949 Say Y here to enable the kernel to panic when it oopses. This 950 has the same effect as setting oops=panic on the kernel command 951 line. 952 953 This feature is useful to ensure that the kernel does not do 954 anything erroneous after an oops which could result in data 955 corruption or other issues. 956 957 Say N if unsure. 958 959config PANIC_ON_OOPS_VALUE 960 int 961 range 0 1 962 default 0 if !PANIC_ON_OOPS 963 default 1 if PANIC_ON_OOPS 964 965config PANIC_TIMEOUT 966 int "panic timeout" 967 default 0 968 help 969 Set the timeout value (in seconds) until a reboot occurs when the 970 the kernel panics. If n = 0, then we wait forever. A timeout 971 value n > 0 will wait n seconds before rebooting, while a timeout 972 value n < 0 will reboot immediately. 973 974config SCHED_DEBUG 975 bool "Collect scheduler debugging info" 976 depends on DEBUG_KERNEL && PROC_FS 977 default y 978 help 979 If you say Y here, the /proc/sched_debug file will be provided 980 that can help debug the scheduler. The runtime overhead of this 981 option is minimal. 982 983config SCHED_INFO 984 bool 985 default n 986 987config SCHEDSTATS 988 bool "Collect scheduler statistics" 989 depends on DEBUG_KERNEL && PROC_FS 990 select SCHED_INFO 991 help 992 If you say Y here, additional code will be inserted into the 993 scheduler and related routines to collect statistics about 994 scheduler behavior and provide them in /proc/schedstat. These 995 stats may be useful for both tuning and debugging the scheduler 996 If you aren't debugging the scheduler or trying to tune a specific 997 application, you can say N to avoid the very slight overhead 998 this adds. 999 1000config SCHED_STACK_END_CHECK 1001 bool "Detect stack corruption on calls to schedule()" 1002 depends on DEBUG_KERNEL 1003 default n 1004 help 1005 This option checks for a stack overrun on calls to schedule(). 1006 If the stack end location is found to be over written always panic as 1007 the content of the corrupted region can no longer be trusted. 1008 This is to ensure no erroneous behaviour occurs which could result in 1009 data corruption or a sporadic crash at a later stage once the region 1010 is examined. The runtime overhead introduced is minimal. 1011 1012config DEBUG_TIMEKEEPING 1013 bool "Enable extra timekeeping sanity checking" 1014 help 1015 This option will enable additional timekeeping sanity checks 1016 which may be helpful when diagnosing issues where timekeeping 1017 problems are suspected. 1018 1019 This may include checks in the timekeeping hotpaths, so this 1020 option may have a (very small) performance impact to some 1021 workloads. 1022 1023 If unsure, say N. 1024 1025config DEBUG_PREEMPT 1026 bool "Debug preemptible kernel" 1027 depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT 1028 default y 1029 help 1030 If you say Y here then the kernel will use a debug variant of the 1031 commonly used smp_processor_id() function and will print warnings 1032 if kernel code uses it in a preemption-unsafe way. Also, the kernel 1033 will detect preemption count underflows. 1034 1035menu "Lock Debugging (spinlocks, mutexes, etc...)" 1036 1037config DEBUG_RT_MUTEXES 1038 bool "RT Mutex debugging, deadlock detection" 1039 depends on DEBUG_KERNEL && RT_MUTEXES 1040 help 1041 This allows rt mutex semantics violations and rt mutex related 1042 deadlocks (lockups) to be detected and reported automatically. 1043 1044config DEBUG_SPINLOCK 1045 bool "Spinlock and rw-lock debugging: basic checks" 1046 depends on DEBUG_KERNEL 1047 select UNINLINE_SPIN_UNLOCK 1048 help 1049 Say Y here and build SMP to catch missing spinlock initialization 1050 and certain other kinds of spinlock errors commonly made. This is 1051 best used in conjunction with the NMI watchdog so that spinlock 1052 deadlocks are also debuggable. 1053 1054config DEBUG_MUTEXES 1055 bool "Mutex debugging: basic checks" 1056 depends on DEBUG_KERNEL 1057 help 1058 This feature allows mutex semantics violations to be detected and 1059 reported. 1060 1061config DEBUG_WW_MUTEX_SLOWPATH 1062 bool "Wait/wound mutex debugging: Slowpath testing" 1063 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1064 select DEBUG_LOCK_ALLOC 1065 select DEBUG_SPINLOCK 1066 select DEBUG_MUTEXES 1067 help 1068 This feature enables slowpath testing for w/w mutex users by 1069 injecting additional -EDEADLK wound/backoff cases. Together with 1070 the full mutex checks enabled with (CONFIG_PROVE_LOCKING) this 1071 will test all possible w/w mutex interface abuse with the 1072 exception of simply not acquiring all the required locks. 1073 Note that this feature can introduce significant overhead, so 1074 it really should not be enabled in a production or distro kernel, 1075 even a debug kernel. If you are a driver writer, enable it. If 1076 you are a distro, do not. 1077 1078config DEBUG_LOCK_ALLOC 1079 bool "Lock debugging: detect incorrect freeing of live locks" 1080 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1081 select DEBUG_SPINLOCK 1082 select DEBUG_MUTEXES 1083 select DEBUG_RT_MUTEXES if RT_MUTEXES 1084 select LOCKDEP 1085 help 1086 This feature will check whether any held lock (spinlock, rwlock, 1087 mutex or rwsem) is incorrectly freed by the kernel, via any of the 1088 memory-freeing routines (kfree(), kmem_cache_free(), free_pages(), 1089 vfree(), etc.), whether a live lock is incorrectly reinitialized via 1090 spin_lock_init()/mutex_init()/etc., or whether there is any lock 1091 held during task exit. 1092 1093config PROVE_LOCKING 1094 bool "Lock debugging: prove locking correctness" 1095 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1096 select LOCKDEP 1097 select DEBUG_SPINLOCK 1098 select DEBUG_MUTEXES 1099 select DEBUG_RT_MUTEXES if RT_MUTEXES 1100 select DEBUG_LOCK_ALLOC 1101 select TRACE_IRQFLAGS 1102 default n 1103 help 1104 This feature enables the kernel to prove that all locking 1105 that occurs in the kernel runtime is mathematically 1106 correct: that under no circumstance could an arbitrary (and 1107 not yet triggered) combination of observed locking 1108 sequences (on an arbitrary number of CPUs, running an 1109 arbitrary number of tasks and interrupt contexts) cause a 1110 deadlock. 1111 1112 In short, this feature enables the kernel to report locking 1113 related deadlocks before they actually occur. 1114 1115 The proof does not depend on how hard and complex a 1116 deadlock scenario would be to trigger: how many 1117 participant CPUs, tasks and irq-contexts would be needed 1118 for it to trigger. The proof also does not depend on 1119 timing: if a race and a resulting deadlock is possible 1120 theoretically (no matter how unlikely the race scenario 1121 is), it will be proven so and will immediately be 1122 reported by the kernel (once the event is observed that 1123 makes the deadlock theoretically possible). 1124 1125 If a deadlock is impossible (i.e. the locking rules, as 1126 observed by the kernel, are mathematically correct), the 1127 kernel reports nothing. 1128 1129 NOTE: this feature can also be enabled for rwlocks, mutexes 1130 and rwsems - in which case all dependencies between these 1131 different locking variants are observed and mapped too, and 1132 the proof of observed correctness is also maintained for an 1133 arbitrary combination of these separate locking variants. 1134 1135 For more details, see Documentation/locking/lockdep-design.txt. 1136 1137config LOCKDEP 1138 bool 1139 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1140 select STACKTRACE 1141 select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !SCORE && !X86 1142 select KALLSYMS 1143 select KALLSYMS_ALL 1144 1145config LOCKDEP_SMALL 1146 bool 1147 1148config LOCK_STAT 1149 bool "Lock usage statistics" 1150 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1151 select LOCKDEP 1152 select DEBUG_SPINLOCK 1153 select DEBUG_MUTEXES 1154 select DEBUG_RT_MUTEXES if RT_MUTEXES 1155 select DEBUG_LOCK_ALLOC 1156 default n 1157 help 1158 This feature enables tracking lock contention points 1159 1160 For more details, see Documentation/locking/lockstat.txt 1161 1162 This also enables lock events required by "perf lock", 1163 subcommand of perf. 1164 If you want to use "perf lock", you also need to turn on 1165 CONFIG_EVENT_TRACING. 1166 1167 CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. 1168 (CONFIG_LOCKDEP defines "acquire" and "release" events.) 1169 1170config DEBUG_LOCKDEP 1171 bool "Lock dependency engine debugging" 1172 depends on DEBUG_KERNEL && LOCKDEP 1173 help 1174 If you say Y here, the lock dependency engine will do 1175 additional runtime checks to debug itself, at the price 1176 of more runtime overhead. 1177 1178config DEBUG_ATOMIC_SLEEP 1179 bool "Sleep inside atomic section checking" 1180 select PREEMPT_COUNT 1181 depends on DEBUG_KERNEL 1182 help 1183 If you say Y here, various routines which may sleep will become very 1184 noisy if they are called inside atomic sections: when a spinlock is 1185 held, inside an rcu read side critical section, inside preempt disabled 1186 sections, inside an interrupt, etc... 1187 1188config DEBUG_LOCKING_API_SELFTESTS 1189 bool "Locking API boot-time self-tests" 1190 depends on DEBUG_KERNEL 1191 help 1192 Say Y here if you want the kernel to run a short self-test during 1193 bootup. The self-test checks whether common types of locking bugs 1194 are detected by debugging mechanisms or not. (if you disable 1195 lock debugging then those bugs wont be detected of course.) 1196 The following locking APIs are covered: spinlocks, rwlocks, 1197 mutexes and rwsems. 1198 1199config LOCK_TORTURE_TEST 1200 tristate "torture tests for locking" 1201 depends on DEBUG_KERNEL 1202 select TORTURE_TEST 1203 default n 1204 help 1205 This option provides a kernel module that runs torture tests 1206 on kernel locking primitives. The kernel module may be built 1207 after the fact on the running kernel to be tested, if desired. 1208 1209 Say Y here if you want kernel locking-primitive torture tests 1210 to be built into the kernel. 1211 Say M if you want these torture tests to build as a module. 1212 Say N if you are unsure. 1213 1214config WW_MUTEX_SELFTEST 1215 tristate "Wait/wound mutex selftests" 1216 help 1217 This option provides a kernel module that runs tests on the 1218 on the struct ww_mutex locking API. 1219 1220 It is recommended to enable DEBUG_WW_MUTEX_SLOWPATH in conjunction 1221 with this test harness. 1222 1223 Say M if you want these self tests to build as a module. 1224 Say N if you are unsure. 1225 1226endmenu # lock debugging 1227 1228config TRACE_IRQFLAGS 1229 bool 1230 help 1231 Enables hooks to interrupt enabling and disabling for 1232 either tracing or lock debugging. 1233 1234config STACKTRACE 1235 bool "Stack backtrace support" 1236 depends on STACKTRACE_SUPPORT 1237 help 1238 This option causes the kernel to create a /proc/pid/stack for 1239 every process, showing its current stack trace. 1240 It is also used by various kernel debugging features that require 1241 stack trace generation. 1242 1243config WARN_ALL_UNSEEDED_RANDOM 1244 bool "Warn for all uses of unseeded randomness" 1245 default n 1246 help 1247 Some parts of the kernel contain bugs relating to their use of 1248 cryptographically secure random numbers before it's actually possible 1249 to generate those numbers securely. This setting ensures that these 1250 flaws don't go unnoticed, by enabling a message, should this ever 1251 occur. This will allow people with obscure setups to know when things 1252 are going wrong, so that they might contact developers about fixing 1253 it. 1254 1255 Unfortunately, on some models of some architectures getting 1256 a fully seeded CRNG is extremely difficult, and so this can 1257 result in dmesg getting spammed for a surprisingly long 1258 time. This is really bad from a security perspective, and 1259 so architecture maintainers really need to do what they can 1260 to get the CRNG seeded sooner after the system is booted. 1261 However, since users can not do anything actionble to 1262 address this, by default the kernel will issue only a single 1263 warning for the first use of unseeded randomness. 1264 1265 Say Y here if you want to receive warnings for all uses of 1266 unseeded randomness. This will be of use primarily for 1267 those developers interersted in improving the security of 1268 Linux kernels running on their architecture (or 1269 subarchitecture). 1270 1271config DEBUG_KOBJECT 1272 bool "kobject debugging" 1273 depends on DEBUG_KERNEL 1274 help 1275 If you say Y here, some extra kobject debugging messages will be sent 1276 to the syslog. 1277 1278config DEBUG_KOBJECT_RELEASE 1279 bool "kobject release debugging" 1280 depends on DEBUG_OBJECTS_TIMERS 1281 help 1282 kobjects are reference counted objects. This means that their 1283 last reference count put is not predictable, and the kobject can 1284 live on past the point at which a driver decides to drop it's 1285 initial reference to the kobject gained on allocation. An 1286 example of this would be a struct device which has just been 1287 unregistered. 1288 1289 However, some buggy drivers assume that after such an operation, 1290 the memory backing the kobject can be immediately freed. This 1291 goes completely against the principles of a refcounted object. 1292 1293 If you say Y here, the kernel will delay the release of kobjects 1294 on the last reference count to improve the visibility of this 1295 kind of kobject release bug. 1296 1297config HAVE_DEBUG_BUGVERBOSE 1298 bool 1299 1300config DEBUG_BUGVERBOSE 1301 bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EXPERT 1302 depends on BUG && (GENERIC_BUG || HAVE_DEBUG_BUGVERBOSE) 1303 default y 1304 help 1305 Say Y here to make BUG() panics output the file name and line number 1306 of the BUG call as well as the EIP and oops trace. This aids 1307 debugging but costs about 70-100K of memory. 1308 1309config DEBUG_LIST 1310 bool "Debug linked list manipulation" 1311 depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION 1312 help 1313 Enable this to turn on extended checks in the linked-list 1314 walking routines. 1315 1316 If unsure, say N. 1317 1318config DEBUG_PI_LIST 1319 bool "Debug priority linked list manipulation" 1320 depends on DEBUG_KERNEL 1321 help 1322 Enable this to turn on extended checks in the priority-ordered 1323 linked-list (plist) walking routines. This checks the entire 1324 list multiple times during each manipulation. 1325 1326 If unsure, say N. 1327 1328config DEBUG_SG 1329 bool "Debug SG table operations" 1330 depends on DEBUG_KERNEL 1331 help 1332 Enable this to turn on checks on scatter-gather tables. This can 1333 help find problems with drivers that do not properly initialize 1334 their sg tables. 1335 1336 If unsure, say N. 1337 1338config DEBUG_NOTIFIERS 1339 bool "Debug notifier call chains" 1340 depends on DEBUG_KERNEL 1341 help 1342 Enable this to turn on sanity checking for notifier call chains. 1343 This is most useful for kernel developers to make sure that 1344 modules properly unregister themselves from notifier chains. 1345 This is a relatively cheap check but if you care about maximum 1346 performance, say N. 1347 1348config DEBUG_CREDENTIALS 1349 bool "Debug credential management" 1350 depends on DEBUG_KERNEL 1351 help 1352 Enable this to turn on some debug checking for credential 1353 management. The additional code keeps track of the number of 1354 pointers from task_structs to any given cred struct, and checks to 1355 see that this number never exceeds the usage count of the cred 1356 struct. 1357 1358 Furthermore, if SELinux is enabled, this also checks that the 1359 security pointer in the cred struct is never seen to be invalid. 1360 1361 If unsure, say N. 1362 1363source "kernel/rcu/Kconfig.debug" 1364 1365config DEBUG_WQ_FORCE_RR_CPU 1366 bool "Force round-robin CPU selection for unbound work items" 1367 depends on DEBUG_KERNEL 1368 default n 1369 help 1370 Workqueue used to implicitly guarantee that work items queued 1371 without explicit CPU specified are put on the local CPU. This 1372 guarantee is no longer true and while local CPU is still 1373 preferred work items may be put on foreign CPUs. Kernel 1374 parameter "workqueue.debug_force_rr_cpu" is added to force 1375 round-robin CPU selection to flush out usages which depend on the 1376 now broken guarantee. This config option enables the debug 1377 feature by default. When enabled, memory and cache locality will 1378 be impacted. 1379 1380config DEBUG_BLOCK_EXT_DEVT 1381 bool "Force extended block device numbers and spread them" 1382 depends on DEBUG_KERNEL 1383 depends on BLOCK 1384 default n 1385 help 1386 BIG FAT WARNING: ENABLING THIS OPTION MIGHT BREAK BOOTING ON 1387 SOME DISTRIBUTIONS. DO NOT ENABLE THIS UNLESS YOU KNOW WHAT 1388 YOU ARE DOING. Distros, please enable this and fix whatever 1389 is broken. 1390 1391 Conventionally, block device numbers are allocated from 1392 predetermined contiguous area. However, extended block area 1393 may introduce non-contiguous block device numbers. This 1394 option forces most block device numbers to be allocated from 1395 the extended space and spreads them to discover kernel or 1396 userland code paths which assume predetermined contiguous 1397 device number allocation. 1398 1399 Note that turning on this debug option shuffles all the 1400 device numbers for all IDE and SCSI devices including libata 1401 ones, so root partition specified using device number 1402 directly (via rdev or root=MAJ:MIN) won't work anymore. 1403 Textual device names (root=/dev/sdXn) will continue to work. 1404 1405 Say N if you are unsure. 1406 1407config CPU_HOTPLUG_STATE_CONTROL 1408 bool "Enable CPU hotplug state control" 1409 depends on DEBUG_KERNEL 1410 depends on HOTPLUG_CPU 1411 default n 1412 help 1413 Allows to write steps between "offline" and "online" to the CPUs 1414 sysfs target file so states can be stepped granular. This is a debug 1415 option for now as the hotplug machinery cannot be stopped and 1416 restarted at arbitrary points yet. 1417 1418 Say N if your are unsure. 1419 1420config NOTIFIER_ERROR_INJECTION 1421 tristate "Notifier error injection" 1422 depends on DEBUG_KERNEL 1423 select DEBUG_FS 1424 help 1425 This option provides the ability to inject artificial errors to 1426 specified notifier chain callbacks. It is useful to test the error 1427 handling of notifier call chain failures. 1428 1429 Say N if unsure. 1430 1431config PM_NOTIFIER_ERROR_INJECT 1432 tristate "PM notifier error injection module" 1433 depends on PM && NOTIFIER_ERROR_INJECTION 1434 default m if PM_DEBUG 1435 help 1436 This option provides the ability to inject artificial errors to 1437 PM notifier chain callbacks. It is controlled through debugfs 1438 interface /sys/kernel/debug/notifier-error-inject/pm 1439 1440 If the notifier call chain should be failed with some events 1441 notified, write the error code to "actions/<notifier event>/error". 1442 1443 Example: Inject PM suspend error (-12 = -ENOMEM) 1444 1445 # cd /sys/kernel/debug/notifier-error-inject/pm/ 1446 # echo -12 > actions/PM_SUSPEND_PREPARE/error 1447 # echo mem > /sys/power/state 1448 bash: echo: write error: Cannot allocate memory 1449 1450 To compile this code as a module, choose M here: the module will 1451 be called pm-notifier-error-inject. 1452 1453 If unsure, say N. 1454 1455config OF_RECONFIG_NOTIFIER_ERROR_INJECT 1456 tristate "OF reconfig notifier error injection module" 1457 depends on OF_DYNAMIC && NOTIFIER_ERROR_INJECTION 1458 help 1459 This option provides the ability to inject artificial errors to 1460 OF reconfig notifier chain callbacks. It is controlled 1461 through debugfs interface under 1462 /sys/kernel/debug/notifier-error-inject/OF-reconfig/ 1463 1464 If the notifier call chain should be failed with some events 1465 notified, write the error code to "actions/<notifier event>/error". 1466 1467 To compile this code as a module, choose M here: the module will 1468 be called of-reconfig-notifier-error-inject. 1469 1470 If unsure, say N. 1471 1472config NETDEV_NOTIFIER_ERROR_INJECT 1473 tristate "Netdev notifier error injection module" 1474 depends on NET && NOTIFIER_ERROR_INJECTION 1475 help 1476 This option provides the ability to inject artificial errors to 1477 netdevice notifier chain callbacks. It is controlled through debugfs 1478 interface /sys/kernel/debug/notifier-error-inject/netdev 1479 1480 If the notifier call chain should be failed with some events 1481 notified, write the error code to "actions/<notifier event>/error". 1482 1483 Example: Inject netdevice mtu change error (-22 = -EINVAL) 1484 1485 # cd /sys/kernel/debug/notifier-error-inject/netdev 1486 # echo -22 > actions/NETDEV_CHANGEMTU/error 1487 # ip link set eth0 mtu 1024 1488 RTNETLINK answers: Invalid argument 1489 1490 To compile this code as a module, choose M here: the module will 1491 be called netdev-notifier-error-inject. 1492 1493 If unsure, say N. 1494 1495config FAULT_INJECTION 1496 bool "Fault-injection framework" 1497 depends on DEBUG_KERNEL 1498 help 1499 Provide fault-injection framework. 1500 For more details, see Documentation/fault-injection/. 1501 1502config FUNCTION_ERROR_INJECTION 1503 def_bool y 1504 depends on HAVE_FUNCTION_ERROR_INJECTION && KPROBES 1505 1506config FAILSLAB 1507 bool "Fault-injection capability for kmalloc" 1508 depends on FAULT_INJECTION 1509 depends on SLAB || SLUB 1510 help 1511 Provide fault-injection capability for kmalloc. 1512 1513config FAIL_PAGE_ALLOC 1514 bool "Fault-injection capabilitiy for alloc_pages()" 1515 depends on FAULT_INJECTION 1516 help 1517 Provide fault-injection capability for alloc_pages(). 1518 1519config FAIL_MAKE_REQUEST 1520 bool "Fault-injection capability for disk IO" 1521 depends on FAULT_INJECTION && BLOCK 1522 help 1523 Provide fault-injection capability for disk IO. 1524 1525config FAIL_IO_TIMEOUT 1526 bool "Fault-injection capability for faking disk interrupts" 1527 depends on FAULT_INJECTION && BLOCK 1528 help 1529 Provide fault-injection capability on end IO handling. This 1530 will make the block layer "forget" an interrupt as configured, 1531 thus exercising the error handling. 1532 1533 Only works with drivers that use the generic timeout handling, 1534 for others it wont do anything. 1535 1536config FAIL_MMC_REQUEST 1537 bool "Fault-injection capability for MMC IO" 1538 depends on FAULT_INJECTION_DEBUG_FS && MMC 1539 help 1540 Provide fault-injection capability for MMC IO. 1541 This will make the mmc core return data errors. This is 1542 useful to test the error handling in the mmc block device 1543 and to test how the mmc host driver handles retries from 1544 the block device. 1545 1546config FAIL_FUTEX 1547 bool "Fault-injection capability for futexes" 1548 select DEBUG_FS 1549 depends on FAULT_INJECTION && FUTEX 1550 help 1551 Provide fault-injection capability for futexes. 1552 1553config FAIL_FUNCTION 1554 bool "Fault-injection capability for functions" 1555 depends on FAULT_INJECTION_DEBUG_FS && FUNCTION_ERROR_INJECTION 1556 help 1557 Provide function-based fault-injection capability. 1558 This will allow you to override a specific function with a return 1559 with given return value. As a result, function caller will see 1560 an error value and have to handle it. This is useful to test the 1561 error handling in various subsystems. 1562 1563config FAULT_INJECTION_DEBUG_FS 1564 bool "Debugfs entries for fault-injection capabilities" 1565 depends on FAULT_INJECTION && SYSFS && DEBUG_FS 1566 help 1567 Enable configuration of fault-injection capabilities via debugfs. 1568 1569config FAULT_INJECTION_STACKTRACE_FILTER 1570 bool "stacktrace filter for fault-injection capabilities" 1571 depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT 1572 depends on !X86_64 1573 select STACKTRACE 1574 select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !SCORE && !X86 1575 help 1576 Provide stacktrace filter for fault-injection capabilities 1577 1578config LATENCYTOP 1579 bool "Latency measuring infrastructure" 1580 depends on DEBUG_KERNEL 1581 depends on STACKTRACE_SUPPORT 1582 depends on PROC_FS 1583 select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !X86 1584 select KALLSYMS 1585 select KALLSYMS_ALL 1586 select STACKTRACE 1587 select SCHEDSTATS 1588 select SCHED_DEBUG 1589 help 1590 Enable this option if you want to use the LatencyTOP tool 1591 to find out which userspace is blocking on what kernel operations. 1592 1593source kernel/trace/Kconfig 1594 1595config PROVIDE_OHCI1394_DMA_INIT 1596 bool "Remote debugging over FireWire early on boot" 1597 depends on PCI && X86 1598 help 1599 If you want to debug problems which hang or crash the kernel early 1600 on boot and the crashing machine has a FireWire port, you can use 1601 this feature to remotely access the memory of the crashed machine 1602 over FireWire. This employs remote DMA as part of the OHCI1394 1603 specification which is now the standard for FireWire controllers. 1604 1605 With remote DMA, you can monitor the printk buffer remotely using 1606 firescope and access all memory below 4GB using fireproxy from gdb. 1607 Even controlling a kernel debugger is possible using remote DMA. 1608 1609 Usage: 1610 1611 If ohci1394_dma=early is used as boot parameter, it will initialize 1612 all OHCI1394 controllers which are found in the PCI config space. 1613 1614 As all changes to the FireWire bus such as enabling and disabling 1615 devices cause a bus reset and thereby disable remote DMA for all 1616 devices, be sure to have the cable plugged and FireWire enabled on 1617 the debugging host before booting the debug target for debugging. 1618 1619 This code (~1k) is freed after boot. By then, the firewire stack 1620 in charge of the OHCI-1394 controllers should be used instead. 1621 1622 See Documentation/debugging-via-ohci1394.txt for more information. 1623 1624config DMA_API_DEBUG 1625 bool "Enable debugging of DMA-API usage" 1626 depends on HAVE_DMA_API_DEBUG 1627 help 1628 Enable this option to debug the use of the DMA API by device drivers. 1629 With this option you will be able to detect common bugs in device 1630 drivers like double-freeing of DMA mappings or freeing mappings that 1631 were never allocated. 1632 1633 This also attempts to catch cases where a page owned by DMA is 1634 accessed by the cpu in a way that could cause data corruption. For 1635 example, this enables cow_user_page() to check that the source page is 1636 not undergoing DMA. 1637 1638 This option causes a performance degradation. Use only if you want to 1639 debug device drivers and dma interactions. 1640 1641 If unsure, say N. 1642 1643menuconfig RUNTIME_TESTING_MENU 1644 bool "Runtime Testing" 1645 1646if RUNTIME_TESTING_MENU 1647 1648config LKDTM 1649 tristate "Linux Kernel Dump Test Tool Module" 1650 depends on DEBUG_FS 1651 depends on BLOCK 1652 default n 1653 help 1654 This module enables testing of the different dumping mechanisms by 1655 inducing system failures at predefined crash points. 1656 If you don't need it: say N 1657 Choose M here to compile this code as a module. The module will be 1658 called lkdtm. 1659 1660 Documentation on how to use the module can be found in 1661 Documentation/fault-injection/provoke-crashes.txt 1662 1663config TEST_LIST_SORT 1664 tristate "Linked list sorting test" 1665 depends on DEBUG_KERNEL || m 1666 help 1667 Enable this to turn on 'list_sort()' function test. This test is 1668 executed only once during system boot (so affects only boot time), 1669 or at module load time. 1670 1671 If unsure, say N. 1672 1673config TEST_SORT 1674 tristate "Array-based sort test" 1675 depends on DEBUG_KERNEL || m 1676 help 1677 This option enables the self-test function of 'sort()' at boot, 1678 or at module load time. 1679 1680 If unsure, say N. 1681 1682config KPROBES_SANITY_TEST 1683 bool "Kprobes sanity tests" 1684 depends on DEBUG_KERNEL 1685 depends on KPROBES 1686 default n 1687 help 1688 This option provides for testing basic kprobes functionality on 1689 boot. A sample kprobe, jprobe and kretprobe are inserted and 1690 verified for functionality. 1691 1692 Say N if you are unsure. 1693 1694config BACKTRACE_SELF_TEST 1695 tristate "Self test for the backtrace code" 1696 depends on DEBUG_KERNEL 1697 default n 1698 help 1699 This option provides a kernel module that can be used to test 1700 the kernel stack backtrace code. This option is not useful 1701 for distributions or general kernels, but only for kernel 1702 developers working on architecture code. 1703 1704 Note that if you want to also test saved backtraces, you will 1705 have to enable STACKTRACE as well. 1706 1707 Say N if you are unsure. 1708 1709config RBTREE_TEST 1710 tristate "Red-Black tree test" 1711 depends on DEBUG_KERNEL 1712 help 1713 A benchmark measuring the performance of the rbtree library. 1714 Also includes rbtree invariant checks. 1715 1716config INTERVAL_TREE_TEST 1717 tristate "Interval tree test" 1718 depends on DEBUG_KERNEL 1719 select INTERVAL_TREE 1720 help 1721 A benchmark measuring the performance of the interval tree library 1722 1723config PERCPU_TEST 1724 tristate "Per cpu operations test" 1725 depends on m && DEBUG_KERNEL 1726 help 1727 Enable this option to build test module which validates per-cpu 1728 operations. 1729 1730 If unsure, say N. 1731 1732config ATOMIC64_SELFTEST 1733 tristate "Perform an atomic64_t self-test" 1734 help 1735 Enable this option to test the atomic64_t functions at boot or 1736 at module load time. 1737 1738 If unsure, say N. 1739 1740config ASYNC_RAID6_TEST 1741 tristate "Self test for hardware accelerated raid6 recovery" 1742 depends on ASYNC_RAID6_RECOV 1743 select ASYNC_MEMCPY 1744 ---help--- 1745 This is a one-shot self test that permutes through the 1746 recovery of all the possible two disk failure scenarios for a 1747 N-disk array. Recovery is performed with the asynchronous 1748 raid6 recovery routines, and will optionally use an offload 1749 engine if one is available. 1750 1751 If unsure, say N. 1752 1753config TEST_HEXDUMP 1754 tristate "Test functions located in the hexdump module at runtime" 1755 1756config TEST_STRING_HELPERS 1757 tristate "Test functions located in the string_helpers module at runtime" 1758 1759config TEST_KSTRTOX 1760 tristate "Test kstrto*() family of functions at runtime" 1761 1762config TEST_PRINTF 1763 tristate "Test printf() family of functions at runtime" 1764 1765config TEST_BITMAP 1766 tristate "Test bitmap_*() family of functions at runtime" 1767 default n 1768 help 1769 Enable this option to test the bitmap functions at boot. 1770 1771 If unsure, say N. 1772 1773config TEST_UUID 1774 tristate "Test functions located in the uuid module at runtime" 1775 1776config TEST_RHASHTABLE 1777 tristate "Perform selftest on resizable hash table" 1778 default n 1779 help 1780 Enable this option to test the rhashtable functions at boot. 1781 1782 If unsure, say N. 1783 1784config TEST_HASH 1785 tristate "Perform selftest on hash functions" 1786 default n 1787 help 1788 Enable this option to test the kernel's integer (<linux/hash.h>), 1789 string (<linux/stringhash.h>), and siphash (<linux/siphash.h>) 1790 hash functions on boot (or module load). 1791 1792 This is intended to help people writing architecture-specific 1793 optimized versions. If unsure, say N. 1794 1795config TEST_PARMAN 1796 tristate "Perform selftest on priority array manager" 1797 default n 1798 depends on PARMAN 1799 help 1800 Enable this option to test priority array manager on boot 1801 (or module load). 1802 1803 If unsure, say N. 1804 1805config TEST_LKM 1806 tristate "Test module loading with 'hello world' module" 1807 default n 1808 depends on m 1809 help 1810 This builds the "test_module" module that emits "Hello, world" 1811 on printk when loaded. It is designed to be used for basic 1812 evaluation of the module loading subsystem (for example when 1813 validating module verification). It lacks any extra dependencies, 1814 and will not normally be loaded by the system unless explicitly 1815 requested by name. 1816 1817 If unsure, say N. 1818 1819config TEST_USER_COPY 1820 tristate "Test user/kernel boundary protections" 1821 default n 1822 depends on m 1823 help 1824 This builds the "test_user_copy" module that runs sanity checks 1825 on the copy_to/from_user infrastructure, making sure basic 1826 user/kernel boundary testing is working. If it fails to load, 1827 a regression has been detected in the user/kernel memory boundary 1828 protections. 1829 1830 If unsure, say N. 1831 1832config TEST_BPF 1833 tristate "Test BPF filter functionality" 1834 default n 1835 depends on m && NET 1836 help 1837 This builds the "test_bpf" module that runs various test vectors 1838 against the BPF interpreter or BPF JIT compiler depending on the 1839 current setting. This is in particular useful for BPF JIT compiler 1840 development, but also to run regression tests against changes in 1841 the interpreter code. It also enables test stubs for eBPF maps and 1842 verifier used by user space verifier testsuite. 1843 1844 If unsure, say N. 1845 1846config FIND_BIT_BENCHMARK 1847 tristate "Test find_bit functions" 1848 default n 1849 help 1850 This builds the "test_find_bit" module that measure find_*_bit() 1851 functions performance. 1852 1853 If unsure, say N. 1854 1855config TEST_FIRMWARE 1856 tristate "Test firmware loading via userspace interface" 1857 default n 1858 depends on FW_LOADER 1859 help 1860 This builds the "test_firmware" module that creates a userspace 1861 interface for testing firmware loading. This can be used to 1862 control the triggering of firmware loading without needing an 1863 actual firmware-using device. The contents can be rechecked by 1864 userspace. 1865 1866 If unsure, say N. 1867 1868config TEST_SYSCTL 1869 tristate "sysctl test driver" 1870 default n 1871 depends on PROC_SYSCTL 1872 help 1873 This builds the "test_sysctl" module. This driver enables to test the 1874 proc sysctl interfaces available to drivers safely without affecting 1875 production knobs which might alter system functionality. 1876 1877 If unsure, say N. 1878 1879config TEST_UDELAY 1880 tristate "udelay test driver" 1881 default n 1882 help 1883 This builds the "udelay_test" module that helps to make sure 1884 that udelay() is working properly. 1885 1886 If unsure, say N. 1887 1888config TEST_STATIC_KEYS 1889 tristate "Test static keys" 1890 default n 1891 depends on m 1892 help 1893 Test the static key interfaces. 1894 1895 If unsure, say N. 1896 1897config TEST_KMOD 1898 tristate "kmod stress tester" 1899 default n 1900 depends on m 1901 depends on BLOCK && (64BIT || LBDAF) # for XFS, BTRFS 1902 depends on NETDEVICES && NET_CORE && INET # for TUN 1903 select TEST_LKM 1904 select XFS_FS 1905 select TUN 1906 select BTRFS_FS 1907 help 1908 Test the kernel's module loading mechanism: kmod. kmod implements 1909 support to load modules using the Linux kernel's usermode helper. 1910 This test provides a series of tests against kmod. 1911 1912 Although technically you can either build test_kmod as a module or 1913 into the kernel we disallow building it into the kernel since 1914 it stress tests request_module() and this will very likely cause 1915 some issues by taking over precious threads available from other 1916 module load requests, ultimately this could be fatal. 1917 1918 To run tests run: 1919 1920 tools/testing/selftests/kmod/kmod.sh --help 1921 1922 If unsure, say N. 1923 1924config TEST_DEBUG_VIRTUAL 1925 tristate "Test CONFIG_DEBUG_VIRTUAL feature" 1926 depends on DEBUG_VIRTUAL 1927 help 1928 Test the kernel's ability to detect incorrect calls to 1929 virt_to_phys() done against the non-linear part of the 1930 kernel's virtual address map. 1931 1932 If unsure, say N. 1933 1934endif # RUNTIME_TESTING_MENU 1935 1936config MEMTEST 1937 bool "Memtest" 1938 depends on HAVE_MEMBLOCK 1939 ---help--- 1940 This option adds a kernel parameter 'memtest', which allows memtest 1941 to be set. 1942 memtest=0, mean disabled; -- default 1943 memtest=1, mean do 1 test pattern; 1944 ... 1945 memtest=17, mean do 17 test patterns. 1946 If you are unsure how to answer this question, answer N. 1947 1948config BUG_ON_DATA_CORRUPTION 1949 bool "Trigger a BUG when data corruption is detected" 1950 select DEBUG_LIST 1951 help 1952 Select this option if the kernel should BUG when it encounters 1953 data corruption in kernel memory structures when they get checked 1954 for validity. 1955 1956 If unsure, say N. 1957 1958source "samples/Kconfig" 1959 1960source "lib/Kconfig.kgdb" 1961 1962source "lib/Kconfig.ubsan" 1963 1964config ARCH_HAS_DEVMEM_IS_ALLOWED 1965 bool 1966 1967config STRICT_DEVMEM 1968 bool "Filter access to /dev/mem" 1969 depends on MMU && DEVMEM 1970 depends on ARCH_HAS_DEVMEM_IS_ALLOWED 1971 default y if TILE || PPC || X86 || ARM64 1972 ---help--- 1973 If this option is disabled, you allow userspace (root) access to all 1974 of memory, including kernel and userspace memory. Accidental 1975 access to this is obviously disastrous, but specific access can 1976 be used by people debugging the kernel. Note that with PAT support 1977 enabled, even in this case there are restrictions on /dev/mem 1978 use due to the cache aliasing requirements. 1979 1980 If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem 1981 file only allows userspace access to PCI space and the BIOS code and 1982 data regions. This is sufficient for dosemu and X and all common 1983 users of /dev/mem. 1984 1985 If in doubt, say Y. 1986 1987config IO_STRICT_DEVMEM 1988 bool "Filter I/O access to /dev/mem" 1989 depends on STRICT_DEVMEM 1990 ---help--- 1991 If this option is disabled, you allow userspace (root) access to all 1992 io-memory regardless of whether a driver is actively using that 1993 range. Accidental access to this is obviously disastrous, but 1994 specific access can be used by people debugging kernel drivers. 1995 1996 If this option is switched on, the /dev/mem file only allows 1997 userspace access to *idle* io-memory ranges (see /proc/iomem) This 1998 may break traditional users of /dev/mem (dosemu, legacy X, etc...) 1999 if the driver using a given range cannot be disabled. 2000 2001 If in doubt, say Y. 2002