[patch 13/13] BLOCK: Fix bad sharing of tag busy list on queues with shared tag maps

[Greg KH <gregkh@suse.de>]

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-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Jens Axboe <jens.axboe@oracle.com>

patch 6eca9004dfcb274a502438a591df5b197690afb1 in mainline.

For the locking to work, only the tag map and tag bit map may be shared
(incidentally, I was just explaining this to Nick yesterday, but I
apparently didn't review the code well enough myself). But we also share
the busy list!  The busy_list must be queue private, or we need a
block_queue_tag covering lock as well.

So we have to move the busy_list to the queue. This'll work fine, and
it'll actually also fix a problem with blk_queue_invalidate_tags() which
will invalidate tags across all shared queues. This is a bit confusing,
the low level driver should call it for each queue seperately since
otherwise you cannot kill tags on just a single queue for eg a hard
drive that stops responding. Since the function has no callers
currently, it's not an issue.

This is fixed with commit 6eca9004dfcb274a502438a591df5b197690afb1 in
Linus' tree.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 block/ll_rw_blk.c      |    8 +++-----
 include/linux/blkdev.h |    2 +-
 2 files changed, 4 insertions(+), 6 deletions(-)

--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -819,7 +819,6 @@ static int __blk_free_tags(struct blk_qu
 	retval = atomic_dec_and_test(&bqt->refcnt);
 	if (retval) {
 		BUG_ON(bqt->busy);
-		BUG_ON(!list_empty(&bqt->busy_list));
 
 		kfree(bqt->tag_index);
 		bqt->tag_index = NULL;
@@ -931,7 +930,6 @@ static struct blk_queue_tag *__blk_queue
 	if (init_tag_map(q, tags, depth))
 		goto fail;
 
-	INIT_LIST_HEAD(&tags->busy_list);
 	tags->busy = 0;
 	atomic_set(&tags->refcnt, 1);
 	return tags;
@@ -982,6 +980,7 @@ int blk_queue_init_tags(struct request_q
 	 */
 	q->queue_tags = tags;
 	q->queue_flags |= (1 << QUEUE_FLAG_QUEUED);
+	INIT_LIST_HEAD(&q->tag_busy_list);
 	return 0;
 fail:
 	kfree(tags);
@@ -1152,7 +1151,7 @@ int blk_queue_start_tag(struct request_q
 	rq->tag = tag;
 	bqt->tag_index[tag] = rq;
 	blkdev_dequeue_request(rq);
-	list_add(&rq->queuelist, &bqt->busy_list);
+	list_add(&rq->queuelist, &q->tag_busy_list);
 	bqt->busy++;
 	return 0;
 }
@@ -1173,11 +1172,10 @@ EXPORT_SYMBOL(blk_queue_start_tag);
  **/
 void blk_queue_invalidate_tags(struct request_queue *q)
 {
-	struct blk_queue_tag *bqt = q->queue_tags;
 	struct list_head *tmp, *n;
 	struct request *rq;
 
-	list_for_each_safe(tmp, n, &bqt->busy_list) {
+	list_for_each_safe(tmp, n, &q->tag_busy_list) {
 		rq = list_entry_rq(tmp);
 
 		if (rq->tag == -1) {
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -356,7 +356,6 @@ enum blk_queue_state {
 struct blk_queue_tag {
 	struct request **tag_index;	/* map of busy tags */
 	unsigned long *tag_map;		/* bit map of free/busy tags */
-	struct list_head busy_list;	/* fifo list of busy tags */
 	int busy;			/* current depth */
 	int max_depth;			/* what we will send to device */
 	int real_max_depth;		/* what the array can hold */
@@ -451,6 +450,7 @@ struct request_queue
 	unsigned int		dma_alignment;
 
 	struct blk_queue_tag	*queue_tags;
+	struct list_head	tag_busy_list;
 
 	unsigned int		nr_sorted;
 	unsigned int		in_flight;

--