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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>
This commit is contained in:
Bart Van Assche 2014-12-09 16:58:11 +01:00 committed by Jens Axboe
parent 45a9c9d909
commit 9e98e9d7cf
1 changed files with 4 additions and 2 deletions
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6
block/blk-mq-tag.c
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@ -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) static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
{ {
int tag, org_last_tag, end; int tag, org_last_tag, end;
bool wrap = last_tag != 0;
org_last_tag = last_tag; org_last_tag = last_tag;
end = bm->depth; end = bm->depth;
@ -148,8 +149,9 @@ restart:
* We started with an offset, start from 0 to * We started with an offset, start from 0 to
* exhaust the map. * exhaust the map.
*/ */
if (org_last_tag && last_tag) { if (wrap) {
end = last_tag; wrap = false;
end = org_last_tag;
last_tag = 0; last_tag = 0;
goto restart; goto restart;
} }