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authorJens Axboe <jens.axboe@oracle.com>2007-09-13 14:26:53 +0200
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-09-13 08:20:25 -0700
commitf3da54ba140c6427fa4a32913e1bf406f41b5dda (patch)
treee39f3c21a06abbf23944e03fc5ec422fc434fc00 /block
parent9ca2152e173554e7ffb7919dc4916a7c61f8be1a (diff)
downloadlinux-linaro-f3da54ba140c6427fa4a32913e1bf406f41b5dda.tar.gz
Fix race with shared tag queue maps
There's a race condition in blk_queue_end_tag() for shared tag maps, users include stex (promise supertrak thingy) and qla2xxx. The former at least has reported bugs in this area, not sure why we haven't seen any for the latter. It could be because the window is narrow and that other conditions in the qla2xxx code hide this. It's a real bug, though, as the stex smp users can attest. We need to ensure two things - the tag bit clearing needs to happen AFTER we cleared the tag pointer, as the tag bit clearing/setting is what protects this map. Secondly, we need to ensure that the visibility of the tag pointer and tag bit clear are ordered properly. [ I removed the SMP barriers - "test_and_clear_bit()" already implies all the required barriers. -- Linus ] Also see http://bugzilla.kernel.org/show_bug.cgi?id=7842 Signed-off-by: Jens Axboe <jens.axboe@oracle.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'block')
-rw-r--r--block/ll_rw_blk.c13
1 files changed, 7 insertions, 6 deletions
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index a15845c164f..cd20367061d 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1075,12 +1075,6 @@ void blk_queue_end_tag(struct request_queue *q, struct request *rq)
*/
return;
- if (unlikely(!__test_and_clear_bit(tag, bqt->tag_map))) {
- printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
- __FUNCTION__, tag);
- return;
- }
-
list_del_init(&rq->queuelist);
rq->cmd_flags &= ~REQ_QUEUED;
rq->tag = -1;
@@ -1090,6 +1084,13 @@ void blk_queue_end_tag(struct request_queue *q, struct request *rq)
__FUNCTION__, tag);
bqt->tag_index[tag] = NULL;
+
+ if (unlikely(!test_and_clear_bit(tag, bqt->tag_map))) {
+ printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
+ __FUNCTION__, tag);
+ return;
+ }
+
bqt->busy--;
}