[3.11.y.z extended stable] Patch "iscsi-target: Fix mutex_trylock usage in iscsit_increment_maxcmdsn" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    iscsi-target: Fix mutex_trylock usage in iscsit_increment_maxcmdsn

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From a31008243f032dd94032f990a4f7195100d248d4 Mon Sep 17 00:00:00 2001
From: Nicholas Bellinger <nab at linux-iscsi.org>
Date: Tue, 12 Nov 2013 17:54:56 -0800
Subject: iscsi-target: Fix mutex_trylock usage in iscsit_increment_maxcmdsn

commit 5e8e6b4b3adebf01a9d97056cbbfd8c44330df99 upstream.

This patch fixes a >= v3.10 regression bug with mutex_trylock() usage
within iscsit_increment_maxcmdsn(), that was originally added to allow
for a special case where ->cmdsn_mutex was already held from the
iscsit_execute_cmd() exception path for ib_isert.

When !mutex_trylock() was occuring under contention during normal RX/TX
process context codepaths, the bug was manifesting itself as the following
protocol error:

  Received CmdSN: 0x000fcbb7 is greater than MaxCmdSN: 0x000fcbb6, protocol error.
  Received CmdSN: 0x000fcbb8 is greater than MaxCmdSN: 0x000fcbb6, protocol error.

This patch simply avoids the direct ib_isert callback in lio_queue_status()
for the special iscsi_execute_cmd() exception cases, that allows the problematic
mutex_trylock() usage in iscsit_increment_maxcmdsn() to go away.

Reported-by: Moussa Ba <moussaba at micron.com>
Tested-by: Moussa Ba <moussaba at micron.com>
Signed-off-by: Nicholas Bellinger <nab at linux-iscsi.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/target/iscsi/iscsi_target_configfs.c | 5 +++++
 drivers/target/iscsi/iscsi_target_device.c   | 6 +-----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target_configfs.c b/drivers/target/iscsi/iscsi_target_configfs.c
index bbfd288..752ee53 100644
--- a/drivers/target/iscsi/iscsi_target_configfs.c
+++ b/drivers/target/iscsi/iscsi_target_configfs.c
@@ -1786,6 +1786,11 @@ static int lio_queue_status(struct se_cmd *se_cmd)
 	struct iscsi_cmd *cmd = container_of(se_cmd, struct iscsi_cmd, se_cmd);

 	cmd->i_state = ISTATE_SEND_STATUS;
+
+	if (cmd->se_cmd.scsi_status || cmd->sense_reason) {
+		iscsit_add_cmd_to_response_queue(cmd, cmd->conn, cmd->i_state);
+		return 0;
+	}
 	cmd->conn->conn_transport->iscsit_queue_status(cmd->conn, cmd);

 	return 0;
diff --git a/drivers/target/iscsi/iscsi_target_device.c b/drivers/target/iscsi/iscsi_target_device.c
index 1b74033..4edcc47 100644
--- a/drivers/target/iscsi/iscsi_target_device.c
+++ b/drivers/target/iscsi/iscsi_target_device.c
@@ -60,11 +60,7 @@ void iscsit_increment_maxcmdsn(struct iscsi_cmd *cmd, struct iscsi_session *sess

 	cmd->maxcmdsn_inc = 1;

-	if (!mutex_trylock(&sess->cmdsn_mutex)) {
-		sess->max_cmd_sn += 1;
-		pr_debug("Updated MaxCmdSN to 0x%08x\n", sess->max_cmd_sn);
-		return;
-	}
+	mutex_lock(&sess->cmdsn_mutex);
 	sess->max_cmd_sn += 1;
 	pr_debug("Updated MaxCmdSN to 0x%08x\n", sess->max_cmd_sn);
 	mutex_unlock(&sess->cmdsn_mutex);
--
1.8.3.2