linux-kernel - [PATCH V2] staging: android: lowmemorykiller: imporve lmk to avoid deadlock issue

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Date:	Mon, 3 Aug 2015 05:53:22 +0000
From:	"Wang, Biao" <biao.wang@...el.com>
To:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"arve@...roid.com" <arve@...roid.com>,
	"riandrews@...roid.com" <riandrews@...roid.com>
CC:	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Zhang, Di" <di.zhang@...el.com>, "Li, Fei" <fei.li@...el.com>,
	"dan.carpenter@...cle.com" <dan.carpenter@...cle.com>,
	"joe@...ches.com" <joe@...ches.com>
Subject: [PATCH V2]  staging: android: lowmemorykiller: imporve lmk to avoid
 deadlock issue

Consider the following case:
Task A trigger lmk with a lock held, while task B try to
get this lock, but unfortunately B is the very culprit task lmk select to
kill. Then B will never be killed, and A will forever select B to kill.
Such dead lock will trigger softlock up issue.

This patch try to pick the next task to break this loop.

Signed-off-by: Wang Biao <biao.wang@...el.com>
Reviewed-by: Zhang Di <di.zhang@...el.com>
Reviewed-by: Dan Carpenter <dan.carpenter@...cle.com>
Reviewed-by: Joe Perches <joe@...ches.com>
---
 drivers/staging/android/lowmemorykiller.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index feafa17..23d9832 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -127,9 +127,10 @@ static unsigned long lowmem_scan(struct shrinker *s, struct shrink_control *sc)
 		if (!p)
 			continue;
 
-		if (test_tsk_thread_flag(p, TIF_MEMDIE) &&
-		    time_before_eq(jiffies, lowmem_deathpending_timeout)) {
+		if (test_tsk_thread_flag(p, TIF_MEMDIE)) {
 			task_unlock(p);
+			if (time_after(jiffies, lowmem_deathpending_timeout)) 
+				continue;
 			rcu_read_unlock();
 			return 0;
 		}
-- 
1.7.9.5

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