linux-kernel - [PATCH v3] scsi: Add timeout to avoid infinite command retry

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Message-ID: <20140211052952.31205.4965.stgit@ltc223.sdl.hitachi.co.jp>
Date:	Tue, 11 Feb 2014 14:29:52 +0900
From:	Eiichi Tsukata <eiichi.tsukata.xh@...achi.com>
To:	JBottomley@...allels.com, linux-scsi@...r.kernel.org
Cc:	clbchenlibo.chen@...wei.com, handai.szj@...il.com,
	linux-kernel@...r.kernel.org, yrl.pp-manager.tt@...achi.com
Subject: [PATCH v3] scsi: Add timeout to avoid infinite command retry

Currently, scsi error handling in scsi_io_completion() tries to
unconditionally requeue scsi command when device keeps some error state.
For example, UNIT_ATTENTION causes infinite retry with
action == ACTION_RETRY.
This is because retryable errors are thought to be temporary and the scsi
device will soon recover from those errors. Normally, such retry policy is
appropriate because the device will soon recover from temporary error state.

But there is no guarantee that device is able to recover from error state
immediately. Some hardware error can prevent device from recovering.

This patch adds timeout in scsi_io_completion() to avoid infinite command
retry in scsi_io_completion(). Once scsi command retry time is longer than
this timeout, the command is treated as failure.

Changes in v3:
 - use existing timeout instead of adding new sysfs attribute
   (Thanks to James)

Changes in v2:
 - check retry timeout in scsi_io_completion() instead of scsi_softirq_done()

Signed-off-by: Eiichi Tsukata <eiichi.tsukata.xh@...achi.com>
Cc: "James E.J. Bottomley" <JBottomley@...allels.com>
Cc: linux-scsi@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 drivers/scsi/scsi_lib.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 7bd7f0d..fa9707d 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -788,6 +788,7 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
 	enum {ACTION_FAIL, ACTION_REPREP, ACTION_RETRY,
 	      ACTION_DELAYED_RETRY} action;
 	char *description = NULL;
+	unsigned long wait_for = (cmd->allowed + 1) * req->timeout;
 
 	if (result) {
 		sense_valid = scsi_command_normalize_sense(cmd, &sshdr);
@@ -989,6 +990,12 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
 		action = ACTION_FAIL;
 	}
 
+	if (action != ACTION_FAIL &&
+	    time_before(cmd->jiffies_at_alloc + wait_for, jiffies)) {
+		action = ACTION_FAIL;
+		description = "Command timed out";
+	}
+
 	switch (action) {
 	case ACTION_FAIL:
 		/* Give up and fail the remainder of the request */

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