oom: avoid deferring oom killer if exiting task is being traced (edd45544) · Commits · 戴 / test

The oom killer naturally defers killing anything if it finds an eligible task that is already exiting and has yet to detach its ->mm. This avoids unnecessarily killing tasks when one is already in the exit path and may free enough memory that the oom killer is no longer needed. This is detected by PF_EXITING since threads that have already detached its ->mm are no longer considered at all. The problem with always deferring when a thread is PF_EXITING, however, is that it may never actually exit when being traced, specifically if another task is tracing it with PTRACE_O_TRACEEXIT. The oom killer does not want to defer in this case since there is no guarantee that thread will ever exit without intervention. This patch will now only defer the oom killer when a thread is PF_EXITING and no ptracer has stopped its progress in the exit path. It also ensures that a child is sacrificed for the chosen parent only if it has a different ->mm as the comment implies: this ensures that the thread group leader is always targeted appropriately. Signed-off-by:

David Rientjes <rientjes@google.com> Reported-by:

Oleg Nesterov <oleg@redhat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Hugh Dickins <hughd@google.com> Cc: Andrey Vagin <avagin@openvz.org> Cc: <stable@kernel.org> [2.6.38.x] Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

+25 −15

Original line number	Diff line number	Diff line
		@@ -31,6 +31,7 @@
		#include <linux/memcontrol.h>
		#include <linux/mempolicy.h>
		#include <linux/security.h>
		#include <linux/ptrace.h>

		int sysctl_panic_on_oom;
		int sysctl_oom_kill_allocating_task;
		@@ -316,22 +317,29 @@ static struct task_struct select_bad_process(unsigned int ppoints,
		if (test_tsk_thread_flag(p, TIF_MEMDIE))
		return ERR_PTR(-1UL);

		if (p->flags & PF_EXITING) {
		/*
		* This is in the process of releasing memory so wait for it
		* to finish before killing some other task by mistake.
		* If p is the current task and is in the process of
		* releasing memory, we allow the "kill" to set
		* TIF_MEMDIE, which will allow it to gain access to
		* memory reserves. Otherwise, it may stall forever.
		*
		* However, if p is the current task, we allow the 'kill' to
		* go ahead if it is exiting: this will simply set TIF_MEMDIE,
		* which will allow it to gain access to memory reserves in
		* the process of exiting and releasing its resources.
		* Otherwise we could get an easy OOM deadlock.
		* The loop isn't broken here, however, in case other
		* threads are found to have already been oom killed.
		*/
		if (p->flags & PF_EXITING) {
		if (p != current)
		return ERR_PTR(-1UL);

		if (p == current) {
		chosen = p;
		*ppoints = 1000;
		} else {
		/*
		* If this task is not being ptraced on exit,
		* then wait for it to finish before killing
		* some other task unnecessarily.
		*/
		if (!(task_ptrace(p->group_leader) &
		PT_TRACE_EXIT))
		return ERR_PTR(-1UL);
		}
		}

		points = oom_badness(p, mem, nodemask, totalpages);
		@@ -493,6 +501,8 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
		list_for_each_entry(child, &t->children, sibling) {
		unsigned int child_points;

		if (child->mm == p->mm)
		continue;
		/*
		* oom_badness() returns 0 if the thread is unkillable
		*/

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