Commit 059af497 authored Sep 21, 2006 by Jens Axboe Committed by Jens Axboe Sep 30, 2006

[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>

parent 0fe23479

block/ll_rw_blk.c

+9 −4

Original line number	Diff line number	Diff line
		@@ -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;

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