linux-kernel - [ 103/180] SCSI: fix eh wakeup (scsi_schedule_eh vs scsi_restart

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Message-Id: <20121001225201.969551571@1wt.eu>
Date:	Tue, 02 Oct 2012 00:53:40 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Dan Williams <dan.j.williams@...el.com>,
	James Bottomley <JBottomley@...allels.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Willy Tarreau <w@....eu>
Subject: [ 103/180] SCSI: fix eh wakeup (scsi_schedule_eh vs scsi_restart_operations)

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@...el.com>

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@...el.com>
Tested-by: Tom Jackson <thomas.p.jackson@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: James Bottomley <JBottomley@...allels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 drivers/scsi/scsi_error.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 573921d..3890793 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -1550,6 +1550,20 @@ 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);
 }
 
 /**
-- 
1.7.2.1.45.g54fbc



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