[PATCH 3.19 106/175] cfq-iosched: handle failure of cfq group allocation

From: Greg Kroah-Hartman
Date: Wed Mar 04 2015 - 01:45:42 EST

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


From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
Fixes: cd1604fab4f9 ("blkcg: factor out blkio_group creation")
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

block/cfq-iosched.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3590,6 +3590,11 @@ 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);

@@ -3626,7 +3631,7 @@ retry:
} else
cfqq = &cfqd->oom_cfqq;
if (new_cfqq)
kmem_cache_free(cfq_pool, new_cfqq);

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