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[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>
This commit is contained in:
Jens Axboe 2006-09-21 20:37:22 +02:00 committed by Jens Axboe
parent 0fe2347957
commit 059af497c2
1 changed files with 9 additions and 4 deletions
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7
block/ll_rw_blk.c
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@ -1171,11 +1171,16 @@ int blk_queue_start_tag(request_queue_t *q, struct request *rq)
BUG();
}
/*
* 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;