diff options
| author | Bart Van Assche <bvanassche@acm.org> | 2014-12-09 16:58:35 +0100 |
|---|---|---|
| committer | Luis Henriques <luis.henriques@canonical.com> | 2015-01-15 10:43:42 +0000 |
| commit | 6148ec1c8840397deae559c07dd3b770e66bd3f3 (patch) | |
| tree | a23324cce0115507abae6113e8d096a00e3fcabb /block | |
| parent | 87a13a346316f60771cad304cbf0c85b5e6f3c04 (diff) | |
blk-mq: Fix a race between bt_clear_tag() and bt_get()
commit c38d185d4af12e8be63ca4b6745d99449c450f12 upstream.
What we need is the following two guarantees:
* Any thread that observes the effect of the test_and_set_bit() by
__bt_get_word() also observes the preceding addition of 'current'
to the appropriate wait list. This is guaranteed by the semantics
of the spin_unlock() operation performed by prepare_and_wait().
Hence the conversion of test_and_set_bit_lock() into
test_and_set_bit().
* The wait lists are examined by bt_clear() after the tag bit has
been cleared. clear_bit_unlock() guarantees that any thread that
observes that the bit has been cleared also observes the store
operations preceding clear_bit_unlock(). However,
clear_bit_unlock() does not prevent that the wait lists are examined
before that the tag bit is cleared. Hence the addition of a memory
barrier between clear_bit() and the wait list examination.
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: Luis Henriques <luis.henriques@canonical.com>
Diffstat (limited to 'block')
| -rw-r--r-- | block/blk-mq-tag.c | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index a1bc33974fc4..1caaa7c4605d 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -158,7 +158,7 @@ restart: return -1; } last_tag = tag + 1; - } while (test_and_set_bit_lock(tag, &bm->word)); + } while (test_and_set_bit(tag, &bm->word)); return tag; } @@ -342,11 +342,10 @@ static void bt_clear_tag(struct blk_mq_bitmap_tags *bt, unsigned int tag) struct bt_wait_state *bs; int wait_cnt; - /* - * The unlock memory barrier need to order access to req in free - * path and clearing tag bit - */ - clear_bit_unlock(TAG_TO_BIT(bt, tag), &bt->map[index].word); + clear_bit(TAG_TO_BIT(bt, tag), &bt->map[index].word); + + /* Ensure that the wait list checks occur after clear_bit(). */ + smp_mb(); bs = bt_wake_ptr(bt); if (!bs) |