[PATCH] blk: remove blk_queue_tag->real_max_depth optimization

blk_queue_tag->real_max_depth was used to optimize out unnecessary
allocations/frees on tag resize.  However, the whole thing was very broken -
tag_map was never allocated to real_max_depth resulting in access beyond the
end of the map, bits in [max_depth..real_max_depth] were set when initializing
a map and copied when resizing resulting in pre-occupied tags.

As the gain of the optimization is very small, well, almost nill, remove the
whole thing.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Acked-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 10 insertions, 26 deletions

diff --git a/drivers/block/ll_rw_blk.c b/drivers/block/ll_rw_blk.c
index 808390c74200..896d17c28f42 100644
--- a/drivers/block/ll_rw_blk.c
+++ b/drivers/block/ll_rw_blk.c
@@ -717,7 +717,7 @@ 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->real_max_depth))
+        if (unlikely(bqt == NULL || tag >= bqt->max_depth))
                 return NULL;
 
         return bqt->tag_index[tag];
@@ -775,9 +775,9 @@ EXPORT_SYMBOL(blk_queue_free_tags);
 static int
 init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
 {
-        int bits, i;
         struct request **tag_index;
         unsigned long *tag_map;
+        int nr_ulongs;
 
         if (depth > q->nr_requests * 2) {
                 depth = q->nr_requests * 2;
@@ -789,24 +789,17 @@ init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
         if (!tag_index)
                 goto fail;
 
-        bits = (depth / BLK_TAGS_PER_LONG) + 1;
-        tag_map = kmalloc(bits * sizeof(unsigned long), GFP_ATOMIC);
+        nr_ulongs = ALIGN(depth, BLK_TAGS_PER_LONG) / BLK_TAGS_PER_LONG;
+        tag_map = kmalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
         if (!tag_map)
                 goto fail;
 
         memset(tag_index, 0, depth * sizeof(struct request *));
-        memset(tag_map, 0, bits * sizeof(unsigned long));
+        memset(tag_map, 0, nr_ulongs * sizeof(unsigned long));
         tags->max_depth = depth;
-        tags->real_max_depth = bits * BITS_PER_LONG;
         tags->tag_index = tag_index;
         tags->tag_map = tag_map;
 
-        /*
-         * set the upper bits if the depth isn't a multiple of the word size
-         */
-        for (i = depth; i < bits * BLK_TAGS_PER_LONG; i++)
-                __set_bit(i, tag_map);
-
         return 0;
 fail:
         kfree(tag_index);
@@ -871,32 +864,24 @@ int blk_queue_resize_tags(request_queue_t *q, int new_depth)
         struct blk_queue_tag *bqt = q->queue_tags;
         struct request **tag_index;
         unsigned long *tag_map;
-        int bits, max_depth;
+        int max_depth, nr_ulongs;
 
         if (!bqt)
                 return -ENXIO;
 
         /*
-         * don't bother sizing down
-         */
-        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->real_max_depth;
+        max_depth = bqt->max_depth;
 
         if (init_tag_map(q, bqt, new_depth))
                 return -ENOMEM;
 
         memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
-        bits = max_depth / BLK_TAGS_PER_LONG;
-        memcpy(bqt->tag_map, tag_map, bits * sizeof(unsigned long));
+        nr_ulongs = ALIGN(max_depth, BLK_TAGS_PER_LONG) / BLK_TAGS_PER_LONG;
+        memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
 
         kfree(tag_index);
         kfree(tag_map);
@@ -926,7 +911,7 @@ void blk_queue_end_tag(request_queue_t *q, struct request *rq)
 
         BUG_ON(tag == -1);
 
-        if (unlikely(tag >= bqt->real_max_depth))
+        if (unlikely(tag >= bqt->max_depth))
                 return;
 
         if (unlikely(!__test_and_clear_bit(tag, bqt->tag_map))) {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 235c3414d268..8d7e2f4151d0 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -294,7 +294,6 @@ 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 */
 };