[PATCH 4/8] mm,oom: Close oom_has_pending_mm race.
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: 2016-07-12 13:31:13
Subsystem:
memory management, memory management - oom killer, the rest · Maintainers:
Andrew Morton, Michal Hocko, Linus Torvalds
Previous patch ignored a situation where oom_has_pending_mm() returns false due to all threads which mm->oom_mm.victim belongs to have reached TASK_DEAD state, for there might be other thread groups sharing that mm. This patch handles such situation by always updating mm->oom_mm.victim. By applying this patch, the comm/pid pair printed at oom_kill_process() and oom_reap_task() might differ. But that will not be a critical problem. Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> --- mm/oom_kill.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 07e8c1a..0b78133 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c@@ -688,6 +688,7 @@ subsys_initcall(oom_init) void mark_oom_victim(struct task_struct *tsk) { struct mm_struct *mm = tsk->mm; + struct task_struct *old_tsk; WARN_ON(oom_killer_disabled); /* OOM killer might race with memcg OOM */
@@ -705,15 +706,26 @@ void mark_oom_victim(struct task_struct *tsk) /* * Since mark_oom_victim() is called from multiple threads, * connect this mm to oom_mm_list only if not yet connected. + * + * But task_in_oom_domain(mm->oom_mm.victim, memcg, nodemask) in + * oom_has_pending_mm() might return false after all threads in one + * thread group (which mm->oom_mm.victim belongs to) reached TASK_DEAD + * state. In that case, the same mm will be selected by another thread + * group (which mm->oom_mm.victim does not belongs to). Therefore, + * we need to replace the old task with the new task (at least when + * task_in_oom_domain() returned false). */ - if (!mm->oom_mm.victim) { + get_task_struct(tsk); + spin_lock(&oom_mm_lock); + old_tsk = mm->oom_mm.victim; + mm->oom_mm.victim = tsk; + if (!old_tsk) { atomic_inc(&mm->mm_count); - get_task_struct(tsk); - mm->oom_mm.victim = tsk; - spin_lock(&oom_mm_lock); list_add_tail(&mm->oom_mm.list, &oom_mm_list); - spin_unlock(&oom_mm_lock); } + spin_unlock(&oom_mm_lock); + if (old_tsk) + put_task_struct(old_tsk); } /**
--
1.8.3.1
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