[PATCH 3.14 02/34] mm/vmpressure.c: fix race in vmpressure_work_fn()

Greg Kroah-Hartman
2014-12-14T20:45:41Z

From: Andrew Morton <akpm@linux-foundation.org>

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@linux-foundation.org: neaten]
Reported-by: ji_ang <ji_ang@163.com>
Cc: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
mm/vmpressure.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -165,6 +165,7 @@ static void vmpressure_work_fn(struct wo
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 wo
* 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;