[SCSI] fix eh wakeup (scsi_schedule_eh vs scsi_restart_operations)

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.

Cc: <stable@vger.kernel.org>
Reported-by: Tom Jackson <thomas.p.jackson@intel.com>
Tested-by: Tom Jackson <thomas.p.jackson@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index d0f71e5d065f..804f63270e37 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -1687,6 +1687,20 @@ 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);
 }
 
 /**