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