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authorMichal Hocko <mhocko@suse.com>2016-07-29 01:44:46 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2016-07-29 02:07:41 +0300
commitb18dc5f291c07ddaf31562b9f27b3a122f1f9b7e (patch)
tree662d9000ce928c625fafa33c71f33c30db2b95bd
parent44a70adec910d6929689e42b6e5cee5b7d202d20 (diff)
downloadlinux-b18dc5f291c07ddaf31562b9f27b3a122f1f9b7e.tar.xz
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: Michal Hocko <mhocko@suse.com> Acked-by: Oleg 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/sched.h26
-rw-r--r--mm/oom_kill.c6
2 files changed, 30 insertions, 2 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d99218a1e043..c0efd80ba40f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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);
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index d8220c5603a5..02da660b7c25 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -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;
}