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

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

From: Bart Van Assche <bart.vanass...@wdc.com>

commit 5fbd545cd3fd311ea1d6e8be4cedddd0ee5684c7 upstream.

Ensure that the members of struct skd_msg_buf have been transferred
to the PCIe adapter before the doorbell is triggered. This patch
avoids that I/O fails sporadically and that the following error
message is reported:

(skd0:STM000196603:[0000:00:09.0]): Completion mismatch comp_id=0x0000 
skreq=0x0400 new=0x0000

Signed-off-by: Bart Van Assche <bart.vanass...@wdc.com>
Cc: Christoph Hellwig <h...@lst.de>
Cc: Hannes Reinecke <h...@suse.de>
Cc: Johannes Thumshirn <jthumsh...@suse.de>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/block/skd_main.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/block/skd_main.c
+++ b/drivers/block/skd_main.c
@@ -2160,6 +2160,9 @@ static void skd_send_fitmsg(struct skd_d
                 */
                qcmd |= FIT_QCMD_MSGSIZE_64;
 
+       /* Make sure skd_msg_buf is written before the doorbell is triggered. */
+       smp_wmb();
+
        SKD_WRITEQ(skdev, qcmd, FIT_Q_COMMAND);
 }
 
@@ -2202,6 +2205,9 @@ static void skd_send_special_fitmsg(stru
        qcmd = skspcl->mb_dma_address;
        qcmd |= FIT_QCMD_QID_NORMAL + FIT_QCMD_MSGSIZE_128;
 
+       /* Make sure skd_msg_buf is written before the doorbell is triggered. */
+       smp_wmb();
+
        SKD_WRITEQ(skdev, qcmd, FIT_Q_COMMAND);
 }
 


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