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| author | Jens Axboe <axboe@kernel.dk> | 2006-09-21 20:37:22 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@nelson.home.kernel.dk> | 2006-09-30 20:52:34 +0200 |
| commit | 059af497c23492cb1ddcbba11c09dad385960bc0 (patch) | |
| tree | 656bbfa7104e065f0da8eac0c14b62ba1c088214 | |
| parent | 0fe23479577124bd2687e6783e39fa0fa4c28005 (diff) | |
| download | lwn-059af497c23492cb1ddcbba11c09dad385960bc0.tar.gz lwn-059af497c23492cb1ddcbba11c09dad385960bc0.zip | |
[PATCH] blk_queue_start_tag() shared map race fix
If we share the tag map between two or more queues, then we cannot
use __set_bit() to set the bit. In fact we need to make sure we
atomically acquire this tag, so loop using test_and_set_bit() to
protect from that.
Noticed by Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
| -rw-r--r-- | block/ll_rw_blk.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c index f757ed413214..83425fb3c8db 100644 --- a/block/ll_rw_blk.c +++ b/block/ll_rw_blk.c @@ -1171,11 +1171,16 @@ int blk_queue_start_tag(request_queue_t *q, struct request *rq) BUG(); } - tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth); - if (tag >= bqt->max_depth) - return 1; + /* + * Protect against shared tag maps, as we may not have exclusive + * access to the tag map. + */ + do { + tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth); + if (tag >= bqt->max_depth) + return 1; - __set_bit(tag, bqt->tag_map); + } while (test_and_set_bit(tag, bqt->tag_map)); rq->cmd_flags |= REQ_QUEUED; rq->tag = tag; |