This is a note to let you know that I've just added the patch titled
SCSI: Fix dm-multipath starvation when scsi host is busy
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
scsi-fix-dm-multipath-starvation-when-scsi-host-is-busy.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From b7e94a1686c5daef4f649f7f4f839cc294f07710 Mon Sep 17 00:00:00 2001
From: Jun'ichi Nomura <[email protected]>
Date: Tue, 22 May 2012 18:57:17 +0900
Subject: SCSI: Fix dm-multipath starvation when scsi host is busy
From: Jun'ichi Nomura <[email protected]>
commit b7e94a1686c5daef4f649f7f4f839cc294f07710 upstream.
block congestion control doesn't have any concept of fairness across
multiple queues. This means that if SCSI reports the host as busy in
the queue congestion control it can result in an unfair starvation
situation in dm-mp if there are multiple multipath devices on the same
host. For example:
http://www.redhat.com/archives/dm-devel/2012-May/msg00123.html
The fix for this is to report only the sdev busy state (and ignore the
host busy state) in the block congestion control call back.
The host is still congested, but the SCSI subsystem will sort out the
congestion in a fair way because it knows the relation between the
queues and the host.
[jejb: fixed up trailing whitespace]
Reported-by: Bernd Schubert <[email protected]>
Tested-by: Bernd Schubert <[email protected]>
Signed-off-by: Jun'ichi Nomura <[email protected]>
Signed-off-by: James Bottomley <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/scsi/scsi_lib.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1378,16 +1378,19 @@ static int scsi_lld_busy(struct request_
{
struct scsi_device *sdev = q->queuedata;
struct Scsi_Host *shost;
- struct scsi_target *starget;
if (!sdev)
return 0;
shost = sdev->host;
- starget = scsi_target(sdev);
- if (scsi_host_in_recovery(shost) || scsi_host_is_busy(shost) ||
- scsi_target_is_busy(starget) || scsi_device_is_busy(sdev))
+ /*
+ * Ignore host/starget busy state.
+ * Since block layer does not have a concept of fairness across
+ * multiple queues, congestion of host/starget needs to be handled
+ * in SCSI layer.
+ */
+ if (scsi_host_in_recovery(shost) || scsi_device_is_busy(sdev))
return 1;
return 0;
Patches currently in stable-queue which might be from [email protected] are
queue-3.4/scsi-fix-dm-multipath-starvation-when-scsi-host-is-busy.patch
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
