[PATCH] cfq: fix NULL pointer dereference in cfq_choose_cfqg.

[Namjae Jeon]

I found null pointer dereferencing possibility while reviewing.
If cfq_get_next_cfqg return null by RB_EMPTY_ROOT, null pointer dereferencing error can occur.

Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxx>
---
 block/cfq-iosched.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index d0ba505..d924272 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2306,7 +2306,7 @@ static void cfq_choose_cfqg(struct cfq_data *cfqd)
 	cfqd->serving_group = cfqg;
 
 	/* Restore the workload type data */
-	if (cfqg->saved_workload_slice) {
+	if (!cfqg && cfqg->saved_workload_slice) {
 		cfqd->workload_expires = jiffies + cfqg->saved_workload_slice;
 		cfqd->serving_type = cfqg->saved_workload;
 		cfqd->serving_prio = cfqg->saved_serving_prio;
-- 
1.7.5.4

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