linux-kernel - [tip:perf/urgent] uprobes: Fix the memcg accounting

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Date:	Thu, 18 Aug 2016 01:07:34 -0700
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	hpa@...or.com, vdavydov@...tuozzo.com, oleg@...hat.com,
	mingo@...nel.org, alexander.shishkin@...ux.intel.com,
	torvalds@...ux-foundation.org, bblanco@...mgrid.com,
	tglx@...utronix.de, acme@...nel.org, jolsa@...hat.com,
	acme@...hat.com, mhocko@...nel.org, hannes@...xchg.org,
	alexei.starovoitov@...il.com, peterz@...radead.org,
	linux-kernel@...r.kernel.org
Subject: [tip:perf/urgent] uprobes: Fix the memcg accounting

Commit-ID:  6c4687cc17a788a6dd8de3e27dbeabb7cbd3e066
Gitweb:     http://git.kernel.org/tip/6c4687cc17a788a6dd8de3e27dbeabb7cbd3e066
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Wed, 17 Aug 2016 17:36:29 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 18 Aug 2016 10:03:26 +0200

uprobes: Fix the memcg accounting

__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.

Reported-and-tested-by: Brenden Blanco <bblanco@...mgrid.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Reviewed-by: Johannes Weiner <hannes@...xchg.org>
Acked-by: Michal Hocko <mhocko@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vladimir Davydov <vdavydov@...tuozzo.com>
Cc: stable@...r.kernel.org # 3.17+
Fixes: 00501b531c47 ("mm: memcontrol: rewrite charge API")
Link: http://lkml.kernel.org/r/20160817153629.GB29724@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/events/uprobes.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index b7a525a..8c50276 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -172,8 +172,10 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
 	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, false);
 		goto unlock;
+	}
 
 	get_page(kpage);
 	page_add_new_anon_rmap(kpage, vma, addr, false);
@@ -200,7 +202,6 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
 
 	err = 0;
  unlock:
-	mem_cgroup_cancel_charge(kpage, memcg, false);
 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
 	unlock_page(page);
 	return err;