linux-kernel - [PATCH 3.2 023/131] Drivers: scsi: storvsc: Implement a eh_timed

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Date:	Thu, 11 Sep 2014 13:32:13 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Christoph Hellwig" <hch@....de>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	"Hannes Reinecke" <hare@...e.de>
Subject: [PATCH 3.2 023/131] Drivers: scsi: storvsc: Implement a
 eh_timed_out handler

3.2.63-rc1 review patch.  If anyone has any objections, please let me know.

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

From: "K. Y. Srinivasan" <kys@...rosoft.com>

commit 56b26e69c8283121febedd12b3cc193384af46b9 upstream.

On Azure, we have seen instances of unbounded I/O latencies. To deal with
this issue, implement handler that can reset the timeout. Note that the
host gaurantees that it will respond to each command that has been issued.

Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
Reviewed-by: Hannes Reinecke <hare@...e.de>
[hch: added a better comment explaining the issue]
Signed-off-by: Christoph Hellwig <hch@....de>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/staging/hv/storvsc_drv.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/drivers/staging/hv/storvsc_drv.c
+++ b/drivers/staging/hv/storvsc_drv.c
@@ -32,6 +32,7 @@
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/hyperv.h>
+#include <linux/blkdev.h>
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>
 #include <scsi/scsi_host.h>
@@ -1129,6 +1130,16 @@ static void storvsc_command_completion(s
 	kmem_cache_free(host_dev->request_pool, cmd_request);
 }
 
+/*
+ * The host guarantees to respond to each command, although I/O latencies might
+ * be unbounded on Azure.  Reset the timer unconditionally to give the host a
+ * chance to perform EH.
+ */
+static enum blk_eh_timer_return storvsc_eh_timed_out(struct scsi_cmnd *scmnd)
+{
+	return BLK_EH_RESET_TIMER;
+}
+
 static bool storvsc_check_scsi_cmd(struct scsi_cmnd *scmnd)
 {
 	bool allowed = true;
@@ -1305,6 +1316,7 @@ static struct scsi_host_template scsi_dr
 	.bios_param =		storvsc_get_chs,
 	.queuecommand =		storvsc_queuecommand,
 	.eh_host_reset_handler =	storvsc_host_reset_handler,
+	.eh_timed_out =		storvsc_eh_timed_out,
 	.slave_alloc =		storvsc_device_alloc,
 	.slave_configure =	storvsc_device_configure,
 	.cmd_per_lun =		1,

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