[3.11.y.z extended stable] Patch "elevator: acquire q->sysfs_lock in elevator_change()" has been added to staging queue

[Luis Henriques]

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

    elevator: acquire q->sysfs_lock in elevator_change()

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 b80b10936d90879f7e365f6484c23ec42b917c67 Mon Sep 17 00:00:00 2001
From: Tomoki Sekiyama <tomoki.sekiyama at hds.com>
Date: Tue, 15 Oct 2013 16:42:19 -0600
Subject: elevator: acquire q->sysfs_lock in elevator_change()

commit 7c8a3679e3d8e9d92d58f282161760a0e247df97 upstream.

Add locking of q->sysfs_lock into elevator_change() (an exported function)
to ensure it is held to protect q->elevator from elevator_init(), even if
elevator_change() is called from non-sysfs paths.
sysfs path (elv_iosched_store) uses __elevator_change(), non-locking
version, as the lock is already taken by elv_iosched_store().

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama at hds.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Cc: Josh Boyer <jwboyer at fedoraproject.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 block/elevator.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/block/elevator.c b/block/elevator.c
index 02d4390..6d765f7 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -965,7 +965,7 @@ fail_init:
 /*
  * Switch this queue to the given IO scheduler.
  */
-int elevator_change(struct request_queue *q, const char *name)
+static int __elevator_change(struct request_queue *q, const char *name)
 {
 	char elevator_name[ELV_NAME_MAX];
 	struct elevator_type *e;
@@ -987,6 +987,18 @@ int elevator_change(struct request_queue *q, const char *name)

 	return elevator_switch(q, e);
 }
+
+int elevator_change(struct request_queue *q, const char *name)
+{
+	int ret;
+
+	/* Protect q->elevator from elevator_init() */
+	mutex_lock(&q->sysfs_lock);
+	ret = __elevator_change(q, name);
+	mutex_unlock(&q->sysfs_lock);
+
+	return ret;
+}
 EXPORT_SYMBOL(elevator_change);

 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
@@ -997,7 +1009,7 @@ ssize_t elv_iosched_store(struct request_queue *q, const char *name,
 	if (!q->elevator)
 		return count;

-	ret = elevator_change(q, name);
+	ret = __elevator_change(q, name);
 	if (!ret)
 		return count;

--
1.8.3.2