There is an error with the medium access timeout feature of the sd driver. The
sdkp->medium_access_timed_out value is set to zero in sd_done() in the wrong
place. It is set to zero only if a command returns sense data. If an I/O
command times out, error handling succeeds, and the I/O commands complete, the
value won't be reset if nothing responds with a sense buffer. Then, another
timeout (no matter how far in the future) can increment it again, causing the
device to be errantly set offline.
The resetting of sdkp->medium_access_timed_out should occur before the check for
sense data.
Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx>
---
It can be reproduced using scsi_debug and using SCSI_DEBUG_OPT_MAC_TIMEOUT to
force some I/O to timeout once. This small script assumes /dev/sdb as
scsi_debug's disk, causes a timeout, completes 2MB of I/O successfully including
the timed out I/O command, then repeats. Without the patch, the device is
offlined on the second loop. All loops will successfully complete I/O
with the patch.
echo "-1" >/sys/bus/pseudo/drivers/scsi_debug/every_nth
for i in `seq 1 4`; do
echo starting loop $i
echo "128" >/sys/bus/pseudo/drivers/scsi_debug/opts
dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=1 &
sleep 5
echo "0" >/sys/bus/pseudo/drivers/scsi_debug/opts
wait
dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=1
echo ending loop $i
done
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 86fcf2c..2779e6b 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1669,12 +1669,12 @@ static int sd_done(struct scsi_cmnd *SCpnt)
sshdr.ascq));
}
#endif
+ sdkp->medium_access_timed_out = 0;
+
if (driver_byte(result) != DRIVER_SENSE &&
(!sense_valid || sense_deferred))
goto out;
- sdkp->medium_access_timed_out = 0;
-
switch (sshdr.sense_key) {
case HARDWARE_ERROR:
case MEDIUM_ERROR:
--
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