linux-kernel - [PATCH 3.16.y-ckt 089/183] cfq-iosched: handle failure of cfq group allocation

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Message-Id: <1425635874-19087-90-git-send-email-luis.henriques@canonical.com>
Date:	Fri,  6 Mar 2015 09:56:20 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Jens Axboe <axboe@...com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 089/183] cfq-iosched: handle failure of cfq group allocation

3.16.7-ckt8 -stable review patch.  If anyone has any objections, please let me know.

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

From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

commit 69abaffec7d47a083739b79e3066cb3730eba72e upstream.

Cfq_lookup_create_cfqg() allocates struct blkcg_gq using GFP_ATOMIC.
In cfq_find_alloc_queue() possible allocation failure is not handled.
As a result kernel oopses on NULL pointer dereference when
cfq_link_cfqq_cfqg() calls cfqg_get() for NULL pointer.

Bug was introduced in v3.5 in commit cd1604fab4f9 ("blkcg: factor
out blkio_group creation"). Prior to that commit cfq group lookup
had returned pointer to root group as fallback.

This patch handles this error using existing fallback oom_cfqq.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Acked-by: Tejun Heo <tj@...nel.org>
Acked-by: Vivek Goyal <vgoyal@...hat.com>
Fixes: cd1604fab4f9 ("blkcg: factor out blkio_group creation")
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 block/cfq-iosched.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f3627ca9303b..2c0585adfaea 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3582,6 +3582,11 @@ retry:
 
 	blkcg = bio_blkcg(bio);
 	cfqg = cfq_lookup_create_cfqg(cfqd, blkcg);
+	if (!cfqg) {
+		cfqq = &cfqd->oom_cfqq;
+		goto out;
+	}
+
 	cfqq = cic_to_cfqq(cic, is_sync);
 
 	/*
@@ -3618,7 +3623,7 @@ retry:
 		} else
 			cfqq = &cfqd->oom_cfqq;
 	}
-
+out:
 	if (new_cfqq)
 		kmem_cache_free(cfq_pool, new_cfqq);
 
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