linux-kernel - [PATCH 4.4 176/192] uprobes: Fix the memcg accounting

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Message-Id: <20160912152206.449718743@linuxfoundation.org>
Date:   Mon, 12 Sep 2016 19:01:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vladimir Davydov <vdavydov@...tuozzo.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.4 176/192] uprobes: Fix the memcg accounting

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@...hat.com>

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.

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>
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/events/uprobes.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -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;