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oom: don't assume that a coredumping thread will exit soon

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oom_kill.c assumes that PF_EXITING task should exit and free the memory
soon.  This is wrong in many ways and one important case is the coredump.
A task can sleep in exit_mm() "forever" while the coredumping sub-thread
can need more memory.

Change the PF_EXITING checks to take SIGNAL_GROUP_COREDUMP into account,
we add the new trivial helper for that.

Note: this is only the first step, this patch doesn't try to solve other
problems.  The SIGNAL_GROUP_COREDUMP check is obviously racy, a task can
participate in coredump after it was already observed in PF_EXITING state,
so TIF_MEMDIE (which also blocks oom-killer) still can be wrongly set.
fatal_signal_pending() can be true because of SIGNAL_GROUP_COREDUMP so
out_of_memory() and mem_cgroup_out_of_memory() shouldn't blindly trust it.
 And even the name/usage of the new helper is confusing, an exiting thread
can only free its ->mm if it is the only/last task in thread group.

[akpm@linux-foundation.org: add comment]
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Tejun Heo <tj@kernel.org>
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 2014-12-12 16:56:24 -08:00 • committed by Linus Torvalds
parent ba914f4815
commit d003f371b2
3 changed files with 15 additions and 4 deletions
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11
include/linux/oom.h
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@ -92,6 +92,17 @@ static inline bool oom_gfp_allowed(gfp_t gfp_mask)
extern struct task_struct *find_lock_task_mm(struct task_struct *p);
static inline bool task_will_free_mem(struct task_struct *task)
{
/*
* A coredumping process may sleep for an extended period in exit_mm(),
* so the oom killer cannot assume that the process will promptly exit
* and release memory.
*/
return (task->flags & PF_EXITING) &&
!(task->signal->flags & SIGNAL_GROUP_COREDUMP);
}
/* sysctls */
extern int sysctl_oom_dump_tasks;
extern int sysctl_oom_kill_allocating_task;