Patch "uprobes: Fix the memcg accounting" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

uprobes: Fix the memcg accounting

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
uprobes-fix-the-memcg-accounting.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Oleg Nesterov <[email protected]>
Date: Wed, 17 Aug 2016 17:36:29 +0200
Subject: uprobes: Fix the memcg accounting

From: Oleg Nesterov <[email protected]>

commit 6c4687cc17a788a6dd8de3e27dbeabb7cbd3e066 upstream.

__replace_page() wronlgy calls mem_cgroup_cancel_charge() in "success" path, it should only do this if page_check_address() fails.

This means that every enable/disable leads to unbalanced mem_cgroup_uncharge() from put_page(old_page), it is trivial to underflow the page_counter->count and trigger OOM.

---
 kernel/events/uprobes.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

@@ -171,8 +171,10 @@ static int __replace_page(struct vm_area
 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
 	err = -EAGAIN;
 	ptep = page_check_address(page, mm, addr, &ptl, 0);
-	if (!ptep)
+	if (!ptep) {
+		mem_cgroup_cancel_charge(kpage, memcg);
 		goto unlock;
+	}
 
 	get_page(kpage);
 	page_add_new_anon_rmap(kpage, vma, addr);

@@ -199,7 +201,6 @@ static int __replace_page(struct vm_area
 
 	err = 0;
  unlock:
-	mem_cgroup_cancel_charge(kpage, memcg);
 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 	unlock_page(page);
 	return err;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/uprobes-fix-the-memcg-accounting.patch queue-4.4/cgroup-reduce-read-locked-section-of-cgroup_threadgroup_rwsem-during-fork.patch