[PATCH 3.16.y-ckt 142/168] mm/vmpressure.c: fix race in vmpressure_work_fn()

From: Luis Henriques
Date: Mon Dec 15 2014 - 09:35:05 EST


3.16.7-ckt3 -stable review patch. If anyone has any objections, please let me know.

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

From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

commit 91b57191cfd152c02ded0745250167d0263084f8 upstream.

In some android devices, there will be a "divide by zero" exception.
vmpr->scanned could be zero before spin_lock(&vmpr->sr_lock).

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=88051

[akpm@xxxxxxxxxxxxxxxxxxxx: neaten]
Reported-by: ji_ang <ji_ang@xxxxxxx>
Cc: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
mm/vmpressure.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index d4042e75f7c7..c5afd573d7da 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -165,6 +165,7 @@ static void vmpressure_work_fn(struct work_struct *work)
unsigned long scanned;
unsigned long reclaimed;

+ spin_lock(&vmpr->sr_lock);
/*
* Several contexts might be calling vmpressure(), so it is
* possible that the work was rescheduled again before the old
@@ -173,11 +174,12 @@ static void vmpressure_work_fn(struct work_struct *work)
* here. No need for any locks here since we don't care if
* vmpr->reclaimed is in sync.
*/
- if (!vmpr->scanned)
+ scanned = vmpr->scanned;
+ if (!scanned) {
+ spin_unlock(&vmpr->sr_lock);
return;
+ }

- spin_lock(&vmpr->sr_lock);
- scanned = vmpr->scanned;
reclaimed = vmpr->reclaimed;
vmpr->scanned = 0;
vmpr->reclaimed = 0;
--
2.1.3

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