[PATCH] sd: retry read_capacity on UNIT_ATTENTION

[hare@suse.de (Hannes Reinecke)]

Hazard testing uncovered yet another bug in sd. Under heavy
reset activity the retry counter might be exhausted and
the command will be returned with sense UNIT_ATTENTION/0x29/00
(POWER ON, RESET, OR BUS DEVICE RESET OCCURRED). In those
cases we should just increase the retry counter again,
retrying one more to clear up this Unit Attention state.

Signed-off-by: Hannes Reinecke <hare@suse.de>

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 1962bea..7d75a21 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1454,8 +1454,15 @@ static int read_capacity_10(struct scsi_disk *sdkp, struct scsi_device *sdp,
 		if (media_not_present(sdkp, &sshdr))
 			return -ENODEV;
 
-		if (the_result)
+		if (the_result) {
 			sense_valid = scsi_sense_valid(&sshdr);
+			if (sense_valid &&
+			    sshdr.sense_key == UNIT_ATTENTION &&
+			    sshdr.asc = 0x29 && sshdr.asq == 0x00)
+			    /* Device reset might occur several times,
+			     * give it one more chance */
+			    retries++;
+		}
 		retries--;
 
 	} while (the_result && retries);