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authorJens Axboe <jens.axboe@oracle.com>2007-09-14 09:57:54 +0200
committerGreg Kroah-Hartman <gregkh@suse.de>2007-09-26 10:54:41 -0700
commitd2f7a9bf48930c25bbd293c28641a8f251c44474 (patch)
parent7eafb2d538dd87b658593b0e7b4429544f866abe (diff)
Fix race with shared tag queue maps
The commit in Linus upstream git tree is f3da54ba140c6427fa4a32913e1bf406f41b5dda. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
1 files changed, 7 insertions, 6 deletions
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index c99b46354859..4369ff2c467d 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -1081,12 +1081,6 @@ void blk_queue_end_tag(request_queue_t *q, struct request *rq)
- 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;
- }
rq->cmd_flags &= ~REQ_QUEUED;
rq->tag = -1;
@@ -1096,6 +1090,13 @@ void blk_queue_end_tag(request_queue_t *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;
+ }