From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Date: Mon, 9 Feb 2015 13:42:49 +0000 (+0300)
Subject: cfq-iosched: handle failure of cfq group allocation
X-Git-Tag: firefly_0821_release~3679^2~778
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=a8ace7cca0c77f9140a25ed175e4d0aaa5d77566;p=firefly-linux-kernel-4.4.55.git

cfq-iosched: handle failure of cfq group allocation

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@yandex-team.ru>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Fixes: cd1604fab4f9 ("blkcg: factor out blkio_group creation")
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c981097dd634..537244c2c7ef 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3575,6 +3575,11 @@ 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);
 
 	/*
@@ -3611,7 +3616,7 @@ retry:
 		} else
 			cfqq = &cfqd->oom_cfqq;
 	}
-
+out:
 	if (new_cfqq)
 		kmem_cache_free(cfq_pool, new_cfqq);