linux-kernel - [PATCH 2/8] cfq-iosched: fix async oom queue handling

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Message-Id: <1433753973-23684-3-git-send-email-tj@kernel.org>
Date:	Mon,  8 Jun 2015 17:59:27 +0900
From:	Tejun Heo <tj@...nel.org>
To:	axboe@...nel.dk
Cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	vgoyal@...hat.com, avanzini.arianna@...il.com,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 2/8] cfq-iosched: fix async oom queue handling

Async cfqq's (cfq_queue's) are shared across cfq_data.  When
cfq_get_queue() obtains a new queue from cfq_find_alloc_queue(), it
stashes the pointer in cfq_data and reuses it from then on; however,
the function doesn't consider that cfq_find_alloc_queue() may return
the oom_cfqq under memory pressure and installs the returned queue
unconditionally.

If the oom_cfqq is installed as an async cfqq, cfq_set_request() will
continue calling cfq_get_queue() hoping to replace it with a proper
queue; however, cfq_get_queue() will keep returning the cached queue
for the slot - the oom_cfqq.

Fix it by skipping caching if the queue is the oom one.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: Arianna Avanzini <avanzini.arianna@...il.com>
---
 block/cfq-iosched.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 2814bb7..c7b33aa 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3683,7 +3683,7 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
 	/*
 	 * pin the queue now that it's allocated, scheduler exit will prune it
 	 */
-	if (!is_sync) {
+	if (!is_sync && cfqq != &cfqd->oom_cfqq) {
 		cfqq->ref++;
 		*async_cfqq = cfqq;
 	}
-- 
2.4.2

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