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mm/oom_kill: fix the wrong task->mm == mm checks in oom_kill_process()

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Both "child->mm == mm" and "p->mm != mm" checks in oom_kill_process() are
wrong.  task->mm can be NULL if the task is the exited group leader.  This
means in particular that "kill sharing same memory" loop can miss a
process with a zombie leader which uses the same ->mm.

Note: the process_has_mm(child, p->mm) check is still not 100% correct,
p->mm can be NULL too.  This is minor, but probably deserves a fix or a
comment anyway.

[akpm@linux-foundation.org: document process_shares_mm() a bit]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Kyle Walker <kwalker@redhat.com>
Cc: Stanislav Kozina <skozina@redhat.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 2015-11-05 18:48:26 -08:00 committed by Linus Torvalds
parent c319025a6c
commit 4d7b3394f7
1 changed files with 20 additions and 2 deletions
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22
mm/oom_kill.c
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@ -474,6 +474,24 @@ void oom_killer_enable(void)
oom_killer_disabled = false;
}
/*
* task->mm can be NULL if the task is the exited group leader. So to
* determine whether the task is using a particular mm, we examine all the
* task's threads: if one of those is using this mm then this task was also
* using it.
*/
static bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
{
struct task_struct *t;
for_each_thread(p, t) {
struct mm_struct *t_mm = READ_ONCE(t->mm);
if (t_mm)
return t_mm == mm;
}
return false;
}
#define K(x) ((x) << (PAGE_SHIFT-10))
/*
* Must be called while holding a reference to p, which will be released upon
@ -521,7 +539,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
list_for_each_entry(child, &t->children, sibling) {
unsigned int child_points;
if (child->mm == p->mm)
if (process_shares_mm(child, p->mm))
continue;
/*
* oom_badness() returns 0 if the thread is unkillable
@ -575,7 +593,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
*/
rcu_read_lock();
for_each_process(p) {
if (p->mm != mm)
if (!process_shares_mm(p, mm))
continue;
if (same_thread_group(p, victim))
continue;