From: Jonathan Lim <jolim@redhat.com>
Date: Wed, 26 Sep 2007 14:38:19 -0400
Subject: [scsi] stale residual on write following BUSY retry
Message-id: 20070926183819.GA18638@sgi-desktop.boston.redhat.com
O-Subject: [RHEL 5.1 PATCH] BZ 300871: stale residual returned on write following BUSY retry
Bugzilla: 300871

A BUSY status returned on a write request results in a stale residual being
returned when the write ultimately successfully completes.

This can be reproduced as follows:

1) issue immediate mode rewind to scsi tape drive
2) issue write request

The tape drive returns busy.  The low level driver detects underrun and sets
the residual into the scsi command.  The low level driver responds with (DID_OK
<< 16) | scsi_status.  scsi_status is 8, hence status_byte(result) == 4, i.e.,
BUSY.

scsi_softirq_done() calls scsi_decide_disposition() which returns
ADD_TO_MLQUEUE.  scsi_softirq_done() then calls scsi_queue_insert() which, on
the way to resubmitting the request to the driver, calls scsi_init_cmd_errh().

The fix modifies scsi_init_cmd_errh() to clear the resid field.  This prevents
a "stale" residual from being returned when the scsi command finally completes
without a BUSY status.

The patch has been successfully included in a kernel build on ia64 and checked
into the scsi-misc tree:

  http://git.kernel.org/?p=linux/kernel/git/jejb/scsi-misc-2.6.git;a=commit;h=2fac3ee0de728a8cc39ee70249f57f46f966b45c

Following is the diff against the 2.6.18-47.el5 kernel source:

Acked-by: Prarit Bhargava <prarit@redhat.com>
---
 drivers/scsi/scsi_lib.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index c109051..a869408 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -443,6 +443,7 @@ EXPORT_SYMBOL_GPL(scsi_execute_async);
 static void scsi_init_cmd_errh(struct scsi_cmnd *cmd)
 {
 	cmd->serial_number = 0;
+	cmd->resid = 0;
 	memset(cmd->sense_buffer, 0, sizeof cmd->sense_buffer);
 	if (cmd->cmd_len == 0)
 		cmd->cmd_len = COMMAND_SIZE(cmd->cmnd[0]);
-- 
1.5.3.5.645.gbb47