linux-kernel - Re: [PATCH] block: Free queue resources at blk_release

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Date:	Tue, 27 Sep 2011 19:15:08 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Hannes Reinecke <hare@...e.de>,
	James Bottomley <James.Bottomley@...allels.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: Free queue resources at blk_release_queue()

On 2011-09-27 18:55, Linus Torvalds wrote:
> On Tue, Sep 27, 2011 at 5:47 PM, Jens Axboe <axboe@...nel.dk> wrote:
>>
>> Do we have acks from the people who saw this oops, that this really does
>> fix it for them? I ask since this fix is vastly cleaner than the other
>> patch floating around, so I'd much rather pull this one in.
> 
> I don't think I can't test it, since it seems to be some hard-to-hit
> race condition. It certainly doesn't seem to happen all the time -
> today was the first time I've seen it on one of my computers.
> 
> But if you forward the actual patch to me (the one I see on lkml seems
> to be broken and doesn't compile cleanly because it's assiging a
> structure to a pointer), I'll try it out anyway.

Thanks, that would be great. It's inlined below.

diff --git a/block/blk-core.c b/block/blk-core.c
index b2ed78a..d34433a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -348,9 +348,10 @@ void blk_put_queue(struct request_queue *q)
 EXPORT_SYMBOL(blk_put_queue);
 
 /*
- * Note: If a driver supplied the queue lock, it should not zap that lock
- * unexpectedly as some queue cleanup components like elevator_exit() and
- * blk_throtl_exit() need queue lock.
+ * Note: If a driver supplied the queue lock, it is disconnected
+ * by this function. The actual state of the lock doesn't matter
+ * here as the request_queue isn't accessible after this point
+ * (QUEUE_FLAG_DEAD is set) and no other requests will be queued.
  */
 void blk_cleanup_queue(struct request_queue *q)
 {
@@ -367,10 +368,8 @@ void blk_cleanup_queue(struct request_queue *q)
 	queue_flag_set_unlocked(QUEUE_FLAG_DEAD, q);
 	mutex_unlock(&q->sysfs_lock);
 
-	if (q->elevator)
-		elevator_exit(q->elevator);
-
-	blk_throtl_exit(q);
+	if (q->queue_lock != &q->__queue_lock)
+		q->queue_lock = &q->__queue_lock;
 
 	blk_put_queue(q);
 }
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e681805..60fda88 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -479,6 +479,11 @@ static void blk_release_queue(struct kobject *kobj)
 
 	blk_sync_queue(q);
 
+	if (q->elevator)
+		elevator_exit(q->elevator);
+
+	blk_throtl_exit(q);
+
 	if (rl->rq_pool)
 		mempool_destroy(rl->rq_pool);
 

-- 
Jens Axboe

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