[PATCH] mmc: core: Add error check to avoid kernel panic caused by NULL pointer

[Corey Gao]

If __mmc_start_req(host, mrq) fails with error, the mrq->cmd->mrq will
be NULL. This will cause kernel panic in the following
mmc_wait_for_req_done(host, mrq). Add error check to cancle unnecessary
mmc_wait_for_req_done(host, mrq) if __mmc_start_req(host, mrq) fails.

Signed-off-by: Corey Gao <gaoce...@gmail.com>
---
 drivers/mmc/core/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 2553d903a82b..b13b484e64aa 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -734,9 +734,11 @@ EXPORT_SYMBOL(mmc_start_req);
  */
 void mmc_wait_for_req(struct mmc_host *host, struct mmc_request *mrq)
 {
-       __mmc_start_req(host, mrq);
+       int err;
 
-       if (!mrq->cap_cmd_during_tfr)
+       err = __mmc_start_req(host, mrq);
+
+       if (!mrq->cap_cmd_during_tfr && !err)
                mmc_wait_for_req_done(host, mrq);
 }
 EXPORT_SYMBOL(mmc_wait_for_req);
-- 
2.17.1