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Commit d003f371 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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oom: don't assume that a coredumping thread will exit soon 



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: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ba914f48

include/linux/oom.h

+11 −0
Original line number Diff line number Diff line
@@ -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;

mm/memcontrol.c

+1 −1
Original line number Diff line number Diff line
@@ -1559,7 +1559,7 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, 
	 * select it.  The goal is to allow it to allocate so that it may

	 * quickly exit and free its memory.

	 */

	if (fatal_signal_pending(current) || current->flags & PF_EXITING) {

	if (fatal_signal_pending(current) || task_will_free_mem(current)) {

		set_thread_flag(TIF_MEMDIE);

		return;

	}

mm/oom_kill.c

+3 −3
Original line number Diff line number Diff line
@@ -281,7 +281,7 @@ enum oom_scan_t oom_scan_process_thread(struct task_struct *task, 
	if (oom_task_origin(task))

		return OOM_SCAN_SELECT;



	if (task->flags & PF_EXITING && !force_kill) {

	if (task_will_free_mem(task) && !force_kill) {

		/*

		 * If this task is not being ptraced on exit, then wait for it

		 * to finish before killing some other task unnecessarily.
@@ -443,7 +443,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, 
	 * If the task is already exiting, don't alarm the sysadmin or kill

	 * its children or threads, just set TIF_MEMDIE so it can die quickly

	 */

	if (p->flags & PF_EXITING) {

	if (task_will_free_mem(p)) {

		set_tsk_thread_flag(p, TIF_MEMDIE);

		put_task_struct(p);

		return;
@@ -649,7 +649,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, 
	 * select it.  The goal is to allow it to allocate so that it may

	 * quickly exit and free its memory.

	 */

	if (fatal_signal_pending(current) || current->flags & PF_EXITING) {

	if (fatal_signal_pending(current) || task_will_free_mem(current)) {

		set_thread_flag(TIF_MEMDIE);

		return;

	}