Commit fa72b903 authored by Tejun Heo's avatar Tejun Heo Committed by Linus Torvalds
Browse files

[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: default avatarTejun Heo <htejun@gmail.com>
Acked-by: default avatarJens Axboe <axboe@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 2bf0fdad

drivers/block/ll_rw_blk.c

+10 −25
Original line number Diff line number Diff line
@@ -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))) {

include/linux/blkdev.h

+0 −1
Original line number Diff line number Diff line
@@ -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 */

};

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