linux-kernel - [PATCH] improve lmk to avoid deadlock issue

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Date:	Thu, 30 Jul 2015 06:49:53 +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>
Subject: [PATCH] improve lmk to avoid deadlock issue

From: "wang, biao" <biao.wang@...el.com>
Date: Thu, 30 Jul 2015 14:14:44 +0800
Subject: [PATCH] improve lmk to avoid deadlock issue

Consider the following case:
Task A trigger lmk with a lock held, while process B try to
get this lock, but unfortunately B is the very culprit Task lmk select to
kill.
So B will never be killed, and A will forever select B to kill and
such dead lock 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>
Signed-off-by: Zhang Di <di.zhang@...el.com>
---
 drivers/staging/android/lowmemorykiller.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
index feafa17..efabeb7 100644
--- a/drivers/staging/android/lowmemorykiller.c
+++ b/drivers/staging/android/lowmemorykiller.c
@@ -127,11 +127,15 @@ 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)) {
-			task_unlock(p);
-			rcu_read_unlock();
-			return 0;
+		if (test_tsk_thread_flag(p, TIF_MEMDIE)) {
+			if (time_before_eq(jiffies, lowmem_deathpending_timeout)) {
+				task_unlock(p);
+				rcu_read_unlock();
+				return 0;
+			} else {
+				task_unlock(p);
+				continue;
+			}
 		}
 		oom_score_adj = p->signal->oom_score_adj;
 		if (oom_score_adj < min_score_adj) {
-- 
1.7.9.5

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