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authorShaohua Li <shli@kernel.org>2013-12-31 11:38:50 +0800
committerJens Axboe <axboe@kernel.dk>2014-01-30 12:57:25 -0700
commitf0276924fa35a3607920a58cf5d878212824b951 (patch)
tree5759cef09f3ba6b2f206ace779fef298a8b9d7be /block/blk-flush.c
parentd835502f3dacad1638d516ab156d66f0ba377cf5 (diff)
blk-mq: Don't reserve a tag for flush request
Reserving a tag (request) for flush to avoid dead lock is a overkill. A tag is valuable resource. We can track the number of flush requests and disallow having too many pending flush requests allocated. With this patch, blk_mq_alloc_request_pinned() could do a busy nop (but not a dead loop) if too many pending requests are allocated and new flush request is allocated. But this should not be a problem, too many pending flush requests are very rare case. I verified this can fix the deadlock caused by too many pending flush requests. Signed-off-by: Shaohua Li <shli@fusionio.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-flush.c')
-rw-r--r--block/blk-flush.c8
1 files changed, 5 insertions, 3 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 9288aaf35c21..9143e85226c7 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -284,9 +284,8 @@ static void mq_flush_work(struct work_struct *work)
q = container_of(work, struct request_queue, mq_flush_work);
- /* We don't need set REQ_FLUSH_SEQ, it's for consistency */
rq = blk_mq_alloc_request(q, WRITE_FLUSH|REQ_FLUSH_SEQ,
- __GFP_WAIT|GFP_ATOMIC, true);
+ __GFP_WAIT|GFP_ATOMIC, false);
rq->cmd_type = REQ_TYPE_FS;
rq->end_io = flush_end_io;
@@ -408,8 +407,11 @@ void blk_insert_flush(struct request *rq)
/*
* @policy now records what operations need to be done. Adjust
* REQ_FLUSH and FUA for the driver.
+ * We keep REQ_FLUSH for mq to track flush requests. For !FUA,
+ * we never dispatch the request directly.
*/
- rq->cmd_flags &= ~REQ_FLUSH;
+ if (rq->cmd_flags & REQ_FUA)
+ rq->cmd_flags &= ~REQ_FLUSH;
if (!(fflags & REQ_FUA))
rq->cmd_flags &= ~REQ_FUA;