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authorJens Axboe <axboe@kernel.dk>2006-09-21 20:37:22 +0200
committerJens Axboe <axboe@nelson.home.kernel.dk>2006-09-30 20:52:34 +0200
commit059af497c23492cb1ddcbba11c09dad385960bc0 (patch)
tree656bbfa7104e065f0da8eac0c14b62ba1c088214 /block/ll_rw_blk.c
parent0fe23479577124bd2687e6783e39fa0fa4c28005 (diff)
downloadlinux-2.6.34-ux500-059af497c23492cb1ddcbba11c09dad385960bc0.tar.gz
[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>
Diffstat (limited to 'block/ll_rw_blk.c')
-rw-r--r--block/ll_rw_blk.c13
1 files changed, 9 insertions, 4 deletions
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index f757ed41321..83425fb3c8d 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;