2 files changed, 16 insertions, 3 deletions

diff --git a/drivers/block/ll_rw_blk.c b/drivers/block/ll_rw_blk.c
index 692a5fced76e..3c818544475e 100644
--- a/drivers/block/ll_rw_blk.c
+++ b/drivers/block/ll_rw_blk.c
@@ -719,7 +719,7 @@ struct request *blk_queue_find_tag(request_queue_t *q, int tag)
 {
         struct blk_queue_tag *bqt = q->queue_tags;
 
-        if (unlikely(bqt == NULL || tag >= bqt->max_depth))
+        if (unlikely(bqt == NULL || tag >= bqt->real_max_depth))
                 return NULL;
 
         return bqt->tag_index[tag];
@@ -798,6 +798,7 @@ init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
 
         memset(tag_index, 0, depth * sizeof(struct request *));
         memset(tag_map, 0, nr_ulongs * sizeof(unsigned long));
+        tags->real_max_depth = depth;
         tags->max_depth = depth;
         tags->tag_index = tag_index;
         tags->tag_map = tag_map;
@@ -872,11 +873,22 @@ int blk_queue_resize_tags(request_queue_t *q, int new_depth)
                 return -ENXIO;
 
         /*
+         * if we already have large enough real_max_depth.  just
+         * adjust max_depth.  *NOTE* as requests with tag value
+         * between new_depth and real_max_depth can be in-flight, tag
+         * map can not be shrunk blindly here.
+         */
+        if (new_depth <= bqt->real_max_depth) {
+                bqt->max_depth = new_depth;
+                return 0;
+        }
+
+        /*
          * save the old state info, so we can copy it back
          */
         tag_index = bqt->tag_index;
         tag_map = bqt->tag_map;
-        max_depth = bqt->max_depth;
+        max_depth = bqt->real_max_depth;
 
         if (init_tag_map(q, bqt, new_depth))
                 return -ENOMEM;
@@ -913,7 +925,7 @@ void blk_queue_end_tag(request_queue_t *q, struct request *rq)
 
         BUG_ON(tag == -1);
 
-        if (unlikely(tag >= bqt->max_depth))
+        if (unlikely(tag >= bqt->real_max_depth))
                 /*
                  * This can happen after tag depth has been reduced.
                  * FIXME: how about a warning or info message here?
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 0881b5cdee3d..19bd8e7e11bf 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -301,6 +301,7 @@ struct blk_queue_tag {
         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 */
         atomic_t refcnt;                /* map can be shared */
 };