xref: /openbmc/linux/mm/oom_kill.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
1 /*
2  *  linux/mm/oom_kill.c
3  *
4  *  Copyright (C)  1998,2000  Rik van Riel
5  *	Thanks go out to Claus Fischer for some serious inspiration and
6  *	for goading me into coding this file...
7  *
8  *  The routines in this file are used to kill a process when
9  *  we're seriously out of memory. This gets called from __alloc_pages()
10  *  in mm/page_alloc.c when we really run out of memory.
11  *
12  *  Since we won't call these routines often (on a well-configured
13  *  machine) this file will double as a 'coding guide' and a signpost
14  *  for newbie kernel hackers. It features several pointers to major
15  *  kernel subsystems and hints as to where to find out what things do.
16  */
17 
18 #include <linux/oom.h>
19 #include <linux/mm.h>
20 #include <linux/sched.h>
21 #include <linux/swap.h>
22 #include <linux/timex.h>
23 #include <linux/jiffies.h>
24 #include <linux/cpuset.h>
25 #include <linux/module.h>
26 #include <linux/notifier.h>
27 
28 int sysctl_panic_on_oom;
29 /* #define DEBUG */
30 
31 /**
32  * badness - calculate a numeric value for how bad this task has been
33  * @p: task struct of which task we should calculate
34  * @uptime: current uptime in seconds
35  *
36  * The formula used is relatively simple and documented inline in the
37  * function. The main rationale is that we want to select a good task
38  * to kill when we run out of memory.
39  *
40  * Good in this context means that:
41  * 1) we lose the minimum amount of work done
42  * 2) we recover a large amount of memory
43  * 3) we don't kill anything innocent of eating tons of memory
44  * 4) we want to kill the minimum amount of processes (one)
45  * 5) we try to kill the process the user expects us to kill, this
46  *    algorithm has been meticulously tuned to meet the principle
47  *    of least surprise ... (be careful when you change it)
48  */
49 
50 unsigned long badness(struct task_struct *p, unsigned long uptime)
51 {
52 	unsigned long points, cpu_time, run_time, s;
53 	struct mm_struct *mm;
54 	struct task_struct *child;
55 
56 	task_lock(p);
57 	mm = p->mm;
58 	if (!mm) {
59 		task_unlock(p);
60 		return 0;
61 	}
62 
63 	/*
64 	 * The memory size of the process is the basis for the badness.
65 	 */
66 	points = mm->total_vm;
67 
68 	/*
69 	 * After this unlock we can no longer dereference local variable `mm'
70 	 */
71 	task_unlock(p);
72 
73 	/*
74 	 * swapoff can easily use up all memory, so kill those first.
75 	 */
76 	if (p->flags & PF_SWAPOFF)
77 		return ULONG_MAX;
78 
79 	/*
80 	 * Processes which fork a lot of child processes are likely
81 	 * a good choice. We add half the vmsize of the children if they
82 	 * have an own mm. This prevents forking servers to flood the
83 	 * machine with an endless amount of children. In case a single
84 	 * child is eating the vast majority of memory, adding only half
85 	 * to the parents will make the child our kill candidate of choice.
86 	 */
87 	list_for_each_entry(child, &p->children, sibling) {
88 		task_lock(child);
89 		if (child->mm != mm && child->mm)
90 			points += child->mm->total_vm/2 + 1;
91 		task_unlock(child);
92 	}
93 
94 	/*
95 	 * CPU time is in tens of seconds and run time is in thousands
96          * of seconds. There is no particular reason for this other than
97          * that it turned out to work very well in practice.
98 	 */
99 	cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
100 		>> (SHIFT_HZ + 3);
101 
102 	if (uptime >= p->start_time.tv_sec)
103 		run_time = (uptime - p->start_time.tv_sec) >> 10;
104 	else
105 		run_time = 0;
106 
107 	s = int_sqrt(cpu_time);
108 	if (s)
109 		points /= s;
110 	s = int_sqrt(int_sqrt(run_time));
111 	if (s)
112 		points /= s;
113 
114 	/*
115 	 * Niced processes are most likely less important, so double
116 	 * their badness points.
117 	 */
118 	if (task_nice(p) > 0)
119 		points *= 2;
120 
121 	/*
122 	 * Superuser processes are usually more important, so we make it
123 	 * less likely that we kill those.
124 	 */
125 	if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
126 				p->uid == 0 || p->euid == 0)
127 		points /= 4;
128 
129 	/*
130 	 * We don't want to kill a process with direct hardware access.
131 	 * Not only could that mess up the hardware, but usually users
132 	 * tend to only have this flag set on applications they think
133 	 * of as important.
134 	 */
135 	if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
136 		points /= 4;
137 
138 	/*
139 	 * If p's nodes don't overlap ours, it may still help to kill p
140 	 * because p may have allocated or otherwise mapped memory on
141 	 * this node before. However it will be less likely.
142 	 */
143 	if (!cpuset_excl_nodes_overlap(p))
144 		points /= 8;
145 
146 	/*
147 	 * Adjust the score by oomkilladj.
148 	 */
149 	if (p->oomkilladj) {
150 		if (p->oomkilladj > 0) {
151 			if (!points)
152 				points = 1;
153 			points <<= p->oomkilladj;
154 		} else
155 			points >>= -(p->oomkilladj);
156 	}
157 
158 #ifdef DEBUG
159 	printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
160 	p->pid, p->comm, points);
161 #endif
162 	return points;
163 }
164 
165 /*
166  * Types of limitations to the nodes from which allocations may occur
167  */
168 #define CONSTRAINT_NONE 1
169 #define CONSTRAINT_MEMORY_POLICY 2
170 #define CONSTRAINT_CPUSET 3
171 
172 /*
173  * Determine the type of allocation constraint.
174  */
175 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
176 {
177 #ifdef CONFIG_NUMA
178 	struct zone **z;
179 	nodemask_t nodes;
180 	int node;
181 
182 	nodes_clear(nodes);
183 	/* node has memory ? */
184 	for_each_online_node(node)
185 		if (NODE_DATA(node)->node_present_pages)
186 			node_set(node, nodes);
187 
188 	for (z = zonelist->zones; *z; z++)
189 		if (cpuset_zone_allowed_softwall(*z, gfp_mask))
190 			node_clear(zone_to_nid(*z), nodes);
191 		else
192 			return CONSTRAINT_CPUSET;
193 
194 	if (!nodes_empty(nodes))
195 		return CONSTRAINT_MEMORY_POLICY;
196 #endif
197 
198 	return CONSTRAINT_NONE;
199 }
200 
201 /*
202  * Simple selection loop. We chose the process with the highest
203  * number of 'points'. We expect the caller will lock the tasklist.
204  *
205  * (not docbooked, we don't want this one cluttering up the manual)
206  */
207 static struct task_struct *select_bad_process(unsigned long *ppoints)
208 {
209 	struct task_struct *g, *p;
210 	struct task_struct *chosen = NULL;
211 	struct timespec uptime;
212 	*ppoints = 0;
213 
214 	do_posix_clock_monotonic_gettime(&uptime);
215 	do_each_thread(g, p) {
216 		unsigned long points;
217 
218 		/*
219 		 * skip kernel threads and tasks which have already released
220 		 * their mm.
221 		 */
222 		if (!p->mm)
223 			continue;
224 		/* skip the init task */
225 		if (is_init(p))
226 			continue;
227 
228 		/*
229 		 * This task already has access to memory reserves and is
230 		 * being killed. Don't allow any other task access to the
231 		 * memory reserve.
232 		 *
233 		 * Note: this may have a chance of deadlock if it gets
234 		 * blocked waiting for another task which itself is waiting
235 		 * for memory. Is there a better alternative?
236 		 */
237 		if (test_tsk_thread_flag(p, TIF_MEMDIE))
238 			return ERR_PTR(-1UL);
239 
240 		/*
241 		 * This is in the process of releasing memory so wait for it
242 		 * to finish before killing some other task by mistake.
243 		 *
244 		 * However, if p is the current task, we allow the 'kill' to
245 		 * go ahead if it is exiting: this will simply set TIF_MEMDIE,
246 		 * which will allow it to gain access to memory reserves in
247 		 * the process of exiting and releasing its resources.
248 		 * Otherwise we could get an easy OOM deadlock.
249 		 */
250 		if (p->flags & PF_EXITING) {
251 			if (p != current)
252 				return ERR_PTR(-1UL);
253 
254 			chosen = p;
255 			*ppoints = ULONG_MAX;
256 		}
257 
258 		if (p->oomkilladj == OOM_DISABLE)
259 			continue;
260 
261 		points = badness(p, uptime.tv_sec);
262 		if (points > *ppoints || !chosen) {
263 			chosen = p;
264 			*ppoints = points;
265 		}
266 	} while_each_thread(g, p);
267 
268 	return chosen;
269 }
270 
271 /**
272  * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO
273  * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
274  * set.
275  */
276 static void __oom_kill_task(struct task_struct *p, int verbose)
277 {
278 	if (is_init(p)) {
279 		WARN_ON(1);
280 		printk(KERN_WARNING "tried to kill init!\n");
281 		return;
282 	}
283 
284 	if (!p->mm) {
285 		WARN_ON(1);
286 		printk(KERN_WARNING "tried to kill an mm-less task!\n");
287 		return;
288 	}
289 
290 	if (verbose)
291 		printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm);
292 
293 	/*
294 	 * We give our sacrificial lamb high priority and access to
295 	 * all the memory it needs. That way it should be able to
296 	 * exit() and clear out its resources quickly...
297 	 */
298 	p->time_slice = HZ;
299 	set_tsk_thread_flag(p, TIF_MEMDIE);
300 
301 	force_sig(SIGKILL, p);
302 }
303 
304 static int oom_kill_task(struct task_struct *p)
305 {
306 	struct mm_struct *mm;
307 	struct task_struct *g, *q;
308 
309 	mm = p->mm;
310 
311 	/* WARNING: mm may not be dereferenced since we did not obtain its
312 	 * value from get_task_mm(p).  This is OK since all we need to do is
313 	 * compare mm to q->mm below.
314 	 *
315 	 * Furthermore, even if mm contains a non-NULL value, p->mm may
316 	 * change to NULL at any time since we do not hold task_lock(p).
317 	 * However, this is of no concern to us.
318 	 */
319 
320 	if (mm == NULL)
321 		return 1;
322 
323 	/*
324 	 * Don't kill the process if any threads are set to OOM_DISABLE
325 	 */
326 	do_each_thread(g, q) {
327 		if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
328 			return 1;
329 	} while_each_thread(g, q);
330 
331 	__oom_kill_task(p, 1);
332 
333 	/*
334 	 * kill all processes that share the ->mm (i.e. all threads),
335 	 * but are in a different thread group. Don't let them have access
336 	 * to memory reserves though, otherwise we might deplete all memory.
337 	 */
338 	do_each_thread(g, q) {
339 		if (q->mm == mm && q->tgid != p->tgid)
340 			force_sig(SIGKILL, q);
341 	} while_each_thread(g, q);
342 
343 	return 0;
344 }
345 
346 static int oom_kill_process(struct task_struct *p, unsigned long points,
347 		const char *message)
348 {
349 	struct task_struct *c;
350 	struct list_head *tsk;
351 
352 	/*
353 	 * If the task is already exiting, don't alarm the sysadmin or kill
354 	 * its children or threads, just set TIF_MEMDIE so it can die quickly
355 	 */
356 	if (p->flags & PF_EXITING) {
357 		__oom_kill_task(p, 0);
358 		return 0;
359 	}
360 
361 	printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
362 					message, p->pid, p->comm, points);
363 
364 	/* Try to kill a child first */
365 	list_for_each(tsk, &p->children) {
366 		c = list_entry(tsk, struct task_struct, sibling);
367 		if (c->mm == p->mm)
368 			continue;
369 		if (!oom_kill_task(c))
370 			return 0;
371 	}
372 	return oom_kill_task(p);
373 }
374 
375 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
376 
377 int register_oom_notifier(struct notifier_block *nb)
378 {
379 	return blocking_notifier_chain_register(&oom_notify_list, nb);
380 }
381 EXPORT_SYMBOL_GPL(register_oom_notifier);
382 
383 int unregister_oom_notifier(struct notifier_block *nb)
384 {
385 	return blocking_notifier_chain_unregister(&oom_notify_list, nb);
386 }
387 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
388 
389 /**
390  * out_of_memory - kill the "best" process when we run out of memory
391  *
392  * If we run out of memory, we have the choice between either
393  * killing a random task (bad), letting the system crash (worse)
394  * OR try to be smart about which process to kill. Note that we
395  * don't have to be perfect here, we just have to be good.
396  */
397 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
398 {
399 	struct task_struct *p;
400 	unsigned long points = 0;
401 	unsigned long freed = 0;
402 	int constraint;
403 
404 	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
405 	if (freed > 0)
406 		/* Got some memory back in the last second. */
407 		return;
408 
409 	if (printk_ratelimit()) {
410 		printk(KERN_WARNING "%s invoked oom-killer: "
411 			"gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
412 			current->comm, gfp_mask, order, current->oomkilladj);
413 		dump_stack();
414 		show_mem();
415 	}
416 
417 	if (sysctl_panic_on_oom == 2)
418 		panic("out of memory. Compulsory panic_on_oom is selected.\n");
419 
420 	/*
421 	 * Check if there were limitations on the allocation (only relevant for
422 	 * NUMA) that may require different handling.
423 	 */
424 	constraint = constrained_alloc(zonelist, gfp_mask);
425 	cpuset_lock();
426 	read_lock(&tasklist_lock);
427 
428 	switch (constraint) {
429 	case CONSTRAINT_MEMORY_POLICY:
430 		oom_kill_process(current, points,
431 				"No available memory (MPOL_BIND)");
432 		break;
433 
434 	case CONSTRAINT_CPUSET:
435 		oom_kill_process(current, points,
436 				"No available memory in cpuset");
437 		break;
438 
439 	case CONSTRAINT_NONE:
440 		if (sysctl_panic_on_oom)
441 			panic("out of memory. panic_on_oom is selected\n");
442 retry:
443 		/*
444 		 * Rambo mode: Shoot down a process and hope it solves whatever
445 		 * issues we may have.
446 		 */
447 		p = select_bad_process(&points);
448 
449 		if (PTR_ERR(p) == -1UL)
450 			goto out;
451 
452 		/* Found nothing?!?! Either we hang forever, or we panic. */
453 		if (!p) {
454 			read_unlock(&tasklist_lock);
455 			cpuset_unlock();
456 			panic("Out of memory and no killable processes...\n");
457 		}
458 
459 		if (oom_kill_process(p, points, "Out of memory"))
460 			goto retry;
461 
462 		break;
463 	}
464 
465 out:
466 	read_unlock(&tasklist_lock);
467 	cpuset_unlock();
468 
469 	/*
470 	 * Give "p" a good chance of killing itself before we
471 	 * retry to allocate memory unless "p" is current
472 	 */
473 	if (!test_thread_flag(TIF_MEMDIE))
474 		schedule_timeout_uninterruptible(1);
475 }
476