[patch -mm] mm, oom: remove oom_lock from exit_mmap

David Rientjes
2018-07-12T21:34:04Z

oom_lock isn't needed for __oom_reap_task_mm(). If MMF_UNSTABLE is
already set for the mm, we can simply back out immediately since oom
reaping is already in progress (or done).

Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/mmap.c | 2 --
mm/oom_kill.c | 6 ++++--
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index cd2431f46188..7f918eb725f6 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3072,9 +3072,7 @@ void exit_mmap(struct mm_struct *mm)
* to mmu_notifier_release(mm) ensures mmu notifier callbacks in
* __oom_reap_task_mm() will not block.
*/
- mutex_lock(&oom_lock);
__oom_reap_task_mm(mm);
- mutex_unlock(&oom_lock);

/*
* Now, set MMF_UNSTABLE to avoid racing with the oom reaper.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 0fe4087d5151..e6328cef090f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -488,9 +488,11 @@ void __oom_reap_task_mm(struct mm_struct *mm)
* Tell all users of get_user/copy_from_user etc... that the content
* is no longer stable. No barriers really needed because unmapping
* should imply barriers already and the reader would hit a page fault
- * if it stumbled over a reaped memory.
+ * if it stumbled over a reaped memory. If MMF_UNSTABLE is already set,
+ * reaping as already occurred so nothing left to do.
*/
- set_bit(MMF_UNSTABLE, &mm->flags);
+ if (test_and_set_bit(MMF_UNSTABLE, &mm->flags))
+ return;

for (vma = mm->mmap ; vma; vma = vma->vm_next) {
if (!can_madv_dontneed_vma(vma))