| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.18 048/150] blk-mq: Avoid that __bt_get_word() wraps multiple times | Date | Tue, 13 Jan 2015 23:21:59 -0800 |
| |
3.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Bart Van Assche <bvanassche@acm.org>
commit 9e98e9d7cf6e9d2ec1cce45e8d5ccaf3f9b386f3 upstream.
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> Signed-off-by: Jens Axboe <axboe@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- block/blk-mq-tag.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -137,6 +137,7 @@ static inline bool hctx_may_queue(struct 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; }
|