Commit b18dc5f2 authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
Browse files

mm, oom: skip vforked tasks from being selected 

vforked tasks are not really sitting on any memory.  They are sharing the
mm with parent until they exec into a new code.  Until then it is just
pinning the address space.  OOM killer will kill the vforked task along
with its parent but we still can end up selecting vforked task when the
parent wouldn't be selected.  E.g.  init doing vfork to launch a task or
vforked being a child of oom unkillable task with an updated oom_score_adj
to be killable.

Add a new helper to check whether a task is in the vfork sharing memory
with its parent and use it in oom_badness to skip over these tasks.

Link: http://lkml.kernel.org/r/1466426628-15074-6-git-send-email-mhocko@kernel.org


Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 44a70ade

include/linux/sched.h

+26 −0
Original line number Diff line number Diff line
@@ -1949,6 +1949,32 @@ static inline int tsk_nr_cpus_allowed(struct task_struct *p) 
#define TNF_FAULT_LOCAL	0x08

#define TNF_MIGRATE_FAIL 0x10



static inline bool in_vfork(struct task_struct *tsk)

{

	bool ret;



	/*

	 * need RCU to access ->real_parent if CLONE_VM was used along with

	 * CLONE_PARENT.

	 *

	 * We check real_parent->mm == tsk->mm because CLONE_VFORK does not

	 * imply CLONE_VM

	 *

	 * CLONE_VFORK can be used with CLONE_PARENT/CLONE_THREAD and thus

	 * ->real_parent is not necessarily the task doing vfork(), so in

	 * theory we can't rely on task_lock() if we want to dereference it.

	 *

	 * And in this case we can't trust the real_parent->mm == tsk->mm

	 * check, it can be false negative. But we do not care, if init or

	 * another oom-unkillable task does this it should blame itself.

	 */

	rcu_read_lock();

	ret = tsk->vfork_done && tsk->real_parent->mm == tsk->mm;

	rcu_read_unlock();



	return ret;

}



#ifdef CONFIG_NUMA_BALANCING

extern void task_numa_fault(int last_node, int node, int pages, int flags);

extern pid_t task_numa_group_id(struct task_struct *p);

mm/oom_kill.c

+4 −2
Original line number Diff line number Diff line
@@ -176,11 +176,13 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg, 


	/*

	 * Do not even consider tasks which are explicitly marked oom

	 * unkillable or have been already oom reaped.

	 * unkillable or have been already oom reaped or the are in

	 * the middle of vfork

	 */

	adj = (long)p->signal->oom_score_adj;

	if (adj == OOM_SCORE_ADJ_MIN ||

			test_bit(MMF_OOM_REAPED, &p->mm->flags)) {

			test_bit(MMF_OOM_REAPED, &p->mm->flags) ||

			in_vfork(p)) {

		task_unlock(p);

		return 0;

	}

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