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

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.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

2 files changed, 4 insertions, 6 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index a8a181072bf8..56f2646612e6 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -791,7 +791,6 @@ 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;
@@ -903,7 +902,6 @@ 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;
@@ -954,6 +952,7 @@ 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);
@@ -1122,7 +1121,7 @@ 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;
 }
@@ -1143,11 +1142,10 @@ 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) {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index bbf906a0b419..8396db24d019 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -341,7 +341,6 @@ 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 */
@@ -435,6 +434,7 @@ 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;