[ 3.5.y.z extended stable ] Patch "iscsi-target: Fix immediate queue starvation regression with" 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 immediate queue starvation regression with

to the linux-3.5.y-queue branch of the 3.5.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-3.5.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 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From beba5d727beeae6f12f12a1df21cfbe413b4a501 Mon Sep 17 00:00:00 2001
From: Nicholas Bellinger <nab at linux-iscsi.org>
Date: Wed, 27 Feb 2013 17:53:52 -0800
Subject: [PATCH] iscsi-target: Fix immediate queue starvation regression with
 DATAIN

commit fd3a9025c0349bc9b01d627529f54e6e1e389015 upstream.

This patch addresses a v3.5+ regression in iscsi-target where TX thread
process context -> handle_response_queue() execution is allowed to run
unbounded while servicing constant outgoing flow of ISTATE_SEND_DATAIN
response state.

This ends up preventing memory release of StatSN acknowledged commands
in a timely manner when under heavy large block streaming DATAIN
workloads.

The regression bug was initially introduced with:

commit 6f3c0e69a9c20441bdc6d3b2d18b83b244384ec6
Author: Andy Grover <agrover at redhat.com>
Date:   Tue Apr 3 15:51:09 2012 -0700

    target/iscsi: Refactor target_tx_thread immediate+response queue loops

Go ahead and follow original iscsi_target_tx_thread() logic and check
to break for immediate queue processing after each DataIN Sequence and/or
Response PDU has been sent.

Reported-by: Benjamin ESTRABAUD <be at mpstor.com>
Cc: Andy Grover <agrover at redhat.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.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index ac41f04..3e7ac0c 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -3608,6 +3608,10 @@ check_rsp_state:
 				spin_lock_bh(&cmd->istate_lock);
 				cmd->i_state = ISTATE_SENT_STATUS;
 				spin_unlock_bh(&cmd->istate_lock);
+
+				if (atomic_read(&conn->check_immediate_queue))
+					return 1;
+
 				continue;
 			} else if (ret == 2) {
 				/* Still must send status,
@@ -3697,7 +3701,7 @@ check_rsp_state:
 		}

 		if (atomic_read(&conn->check_immediate_queue))
-			break;
+			return 1;
 	}

 	return 0;
@@ -3741,12 +3745,15 @@ restart:
 		     signal_pending(current))
 			goto transport_err;

+get_immediate:
 		ret = handle_immediate_queue(conn);
 		if (ret < 0)
 			goto transport_err;

 		ret = handle_response_queue(conn);
-		if (ret == -EAGAIN)
+		if (ret == 1)
+			goto get_immediate;
+		else if (ret == -EAGAIN)
 			goto restart;
 		else if (ret < 0)
 			goto transport_err;
--
1.8.1.2