[PATCH -mm] mmoom-fix-potentially-killing-unrelated-process-fix
From: Oleg Nesterov
Date: Tue Oct 06 2015 - 12:31:27 EST
oom_kill_process() does atomic_inc(&mm->mm_users) to ensure that
this ->mm can't go away and this is wrong, change it to rely on
->mm_count and mmdrop().
Firstly, we do not want to delay exit_mmap/etc if the victim exits
before we do mmput(), but this is minor.
More importantly, we simply can not do mmput() in oom_kill_process(),
this can deadlock if (for example) the caller holds i_mmap_rwsem and
mmput() actually leads to exit_mmap(); the victim can have this file
mmaped and in this case unmap_vmas/free_pgtables paths will take the
same lock for writing. And at least huge_pmd_share() does pmd_alloc()
under i_mmap_rwsem because VM_HUGETLB memory is not reclaimable.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
mm/oom_kill.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 034d219..52abb78 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -571,7 +571,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
/* Get a reference to safely compare mm after task_unlock(victim) */
mm = victim->mm;
- atomic_inc(&mm->mm_users);
+ atomic_inc(&mm->mm_count);
/*
* We should send SIGKILL before setting TIF_MEMDIE in order to prevent
* the OOM victim from depleting the memory reserves from the user
@@ -609,7 +609,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
}
rcu_read_unlock();
- mmput(mm);
+ mmdrop(mm);
put_task_struct(victim);
}
#undef K
--
2.4.3
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