Commit 9e98e9d7 authored Dec 09, 2014 by Bart Van Assche Committed by Jens Axboe Dec 09, 2014

blk-mq: Avoid that __bt_get_word() wraps multiple times



If __bt_get_word() is called with last_tag != 0, if the first
find_next_zero_bit() fails, if after wrap-around the
test_and_set_bit() call fails and find_next_zero_bit() succeeds,
if the next test_and_set_bit() call fails and subsequently
find_next_zero_bit() does not find a zero bit, then another
wrap-around will occur. Avoid this by introducing an additional
local variable.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Robert Elliott <elliott@hp.com>
Cc: Ming Lei <ming.lei@canonical.com>
Cc: Alexander Gordeev <agordeev@redhat.com>
Cc: <stable@vger.kernel.org> # v3.13+
Signed-off-by: Jens Axboe <axboe@fb.com>

parent 45a9c9d9

block/blk-mq-tag.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -137,6 +137,7 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
		static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
		{
		int tag, org_last_tag, end;
		bool wrap = last_tag != 0;

		org_last_tag = last_tag;
		end = bm->depth;
		@@ -148,8 +149,9 @@ restart:
		* We started with an offset, start from 0 to
		* exhaust the map.
		*/
		if (org_last_tag && last_tag) {
		end = last_tag;
		if (wrap) {
		wrap = false;
		end = org_last_tag;
		last_tag = 0;
		goto restart;
		}