Drivers: scsi: storvsc: Implement a eh_timed_out handler

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 <[e-mail]>
Reviewed-by: Hannes Reinecke <[e-mail]>
Cc: <[e-mail]>
[hch: added a better comment explaining the issue]
Signed-off-by: Christoph Hellwig <[e-mail]>

drivers/scsi/storvsc_drv.c

···
 #include <linux/device.h>
 #include <linux/hyperv.h>
 #include <linux/mempool.h>
+#include <linux/blkdev.h>
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>
 #include <scsi/scsi_host.h>
···
 	return SUCCESS;
 }
 
+/*
+ * 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_scsi_cmd_ok(struct scsi_cmnd *scmnd)
 {
 	bool allowed = true;
···
 	.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_destroy =	storvsc_device_destroy,
 	.slave_configure =	storvsc_device_configure,