mm/oom_kill: fix the wrong task->mm == mm checks in oom_kill_process() (4d7b3394) · Commits · 戴 / test

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>

mm/oom_kill.c

+20 −2

Original line number	Diff line number	Diff line
		@@ -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;

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