BLOCK: Fix bad sharing of tag busy list on queues with shared tag maps

patch 6eca9004 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 6eca9004 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

@@ -819,7 +819,6 @@ static int __blk_free_tags(struct blk_queue_tag *bqt)
 	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_init_tags(struct request_queue *q,
 	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_queue *q, int depth,
 	 */
 	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_queue *q, struct request *rq)
 	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) {

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;