[v2.6.34-stable 207/213] fix eh wakeup (scsi_schedule_eh vs scsi_restart_operations)

[Paul Gortmaker]

From: Dan Williams <dan.j.williams@xxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 57fc2e335fd3c2f898ee73570dc81426c28dc7b4 upstream.

Rapid ata hotplug on a libsas controller results in cases where libsas
is waiting indefinitely on eh to perform an ata probe.

A race exists between scsi_schedule_eh() and scsi_restart_operations()
in the case when scsi_restart_operations() issues i/o to other devices
in the sas domain.  When this happens the host state transitions from
SHOST_RECOVERY (set by scsi_schedule_eh) back to SHOST_RUNNING and
->host_busy is non-zero so we put the eh thread to sleep even though
->host_eh_scheduled is active.

Before putting the error handler to sleep we need to check if the
host_state needs to return to SHOST_RECOVERY for another trip through
eh.  Since i/o that is released by scsi_restart_operations has been
blocked for at least one eh cycle, this implementation allows those
i/o's to run before another eh cycle starts to discourage hung task
timeouts.

Reported-by: Tom Jackson <thomas.p.jackson@xxxxxxxxx>
Tested-by: Tom Jackson <thomas.p.jackson@xxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: James Bottomley <JBottomley@xxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 drivers/scsi/scsi_error.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 7ad53fa42766..3a56835c3ad3 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -1614,6 +1614,20 @@ static void scsi_restart_operations(struct Scsi_Host *shost)
 	 * requests are started.
 	 */
 	scsi_run_host_queues(shost);
+
+	/*
+	 * if eh is active and host_eh_scheduled is pending we need to re-run
+	 * recovery.  we do this check after scsi_run_host_queues() to allow
+	 * everything pent up since the last eh run a chance to make forward
+	 * progress before we sync again.  Either we'll immediately re-run
+	 * recovery or scsi_device_unbusy() will wake us again when these
+	 * pending commands complete.
+	 */
+	spin_lock_irqsave(shost->host_lock, flags);
+	if (shost->host_eh_scheduled)
+		if (scsi_host_set_state(shost, SHOST_RECOVERY))
+			WARN_ON(scsi_host_set_state(shost, SHOST_CANCEL_RECOVERY));
+	spin_unlock_irqrestore(shost->host_lock, flags);
 }
 
 /**
-- 
1.8.5.2

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