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oom: introduce find_lock_task_mm() to fix !mm false positives

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Almost all ->mm == NULL checks in oom_kill.c are wrong.

The current code assumes that the task without ->mm has already released
its memory and ignores the process.  However this is not necessarily true
when this process is multithreaded, other live sub-threads can use this
->mm.

- Remove the "if (!p->mm)" check in select_bad_process(), it is
  just wrong.

- Add the new helper, find_lock_task_mm(), which finds the live
  thread which uses the memory and takes task_lock() to pin ->mm

- change oom_badness() to use this helper instead of just checking
  ->mm != NULL.

- As David pointed out, select_bad_process() must never choose the
  task without ->mm, but no matter what oom_badness() returns the
  task can be chosen if nothing else has been found yet.

  Change oom_badness() to return int, change it to return -1 if
  find_lock_task_mm() fails, and change select_bad_process() to
  check points >= 0.

Note! This patch is not enough, we need more changes.

	- oom_badness() was fixed, but oom_kill_task() still ignores
	  the task without ->mm

	- oom_forkbomb_penalty() should use find_lock_task_mm() too,
	  and it also needs other changes to actually find the first
	  first-descendant children

This will be addressed later.

[kosaki.motohiro@jp.fujitsu.com: use in badness(), __oom_kill_task()]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2010-08-09 17:18:45 -07:00 committed by Linus Torvalds
parent b52279406e
commit dd8e8f405c
1 changed files with 43 additions and 31 deletions
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74
mm/oom_kill.c
View file

@ -52,6 +52,20 @@ static int has_intersects_mems_allowed(struct task_struct *tsk)
return 0;
}
static struct task_struct *find_lock_task_mm(struct task_struct *p)
{
struct task_struct *t = p;
do {
task_lock(t);
if (likely(t->mm))
return t;
task_unlock(t);
} while_each_thread(p, t);
return NULL;
}
/**
* badness - calculate a numeric value for how bad this task has been
* @p: task struct of which task we should calculate
@ -74,8 +88,8 @@ static int has_intersects_mems_allowed(struct task_struct *tsk)
unsigned long badness(struct task_struct *p, unsigned long uptime)
{
unsigned long points, cpu_time, run_time;
struct mm_struct *mm;
struct task_struct *child;
struct task_struct *c, *t;
int oom_adj = p->signal->oom_adj;
struct task_cputime task_time;
unsigned long utime;
@ -84,17 +98,14 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
if (oom_adj == OOM_DISABLE)
return 0;
task_lock(p);
mm = p->mm;
if (!mm) {
task_unlock(p);
p = find_lock_task_mm(p);
if (!p)
return 0;
}
/*
* The memory size of the process is the basis for the badness.
*/
points = mm->total_vm;
points = p->mm->total_vm;
/*
* After this unlock we can no longer dereference local variable `mm'
@ -115,12 +126,17 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
* child is eating the vast majority of memory, adding only half
* to the parents will make the child our kill candidate of choice.
*/
list_for_each_entry(child, &p->children, sibling) {
task_lock(child);
if (child->mm != mm && child->mm)
points += child->mm->total_vm/2 + 1;
task_unlock(child);
}
t = p;
do {
list_for_each_entry(c, &t->children, sibling) {
child = find_lock_task_mm(c);
if (child) {
if (child->mm != p->mm)
points += child->mm->total_vm/2 + 1;
task_unlock(child);
}
}
} while_each_thread(p, t);
/*
* CPU time is in tens of seconds and run time is in thousands
@ -256,9 +272,6 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
for_each_process(p) {
unsigned long points;
/* skip tasks that have already released their mm */
if (!p->mm)
continue;
/* skip the init task and kthreads */
if (is_global_init(p) || (p->flags & PF_KTHREAD))
continue;
@ -385,14 +398,9 @@ static void __oom_kill_task(struct task_struct *p, int verbose)
return;
}
task_lock(p);
if (!p->mm) {
WARN_ON(1);
printk(KERN_WARNING "tried to kill an mm-less task %d (%s)!\n",
task_pid_nr(p), p->comm);
task_unlock(p);
p = find_lock_task_mm(p);
if (!p)
return;
}
if (verbose)
printk(KERN_ERR "Killed process %d (%s) "
@ -437,6 +445,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
const char *message)
{
struct task_struct *c;
struct task_struct *t = p;
if (printk_ratelimit())
dump_header(p, gfp_mask, order, mem);
@ -454,14 +463,17 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
message, task_pid_nr(p), p->comm, points);
/* Try to kill a child first */
list_for_each_entry(c, &p->children, sibling) {
if (c->mm == p->mm)
continue;
if (mem && !task_in_mem_cgroup(c, mem))
continue;
if (!oom_kill_task(c))
return 0;
}
do {
list_for_each_entry(c, &t->children, sibling) {
if (c->mm == p->mm)
continue;
if (mem && !task_in_mem_cgroup(c, mem))
continue;
if (!oom_kill_task(c))
return 0;
}
} while_each_thread(p, t);
return oom_kill_task(p);
}