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authorMing Lei <tom.leiming@gmail.com>2016-10-26 16:57:15 +0800
committerJens Axboe <axboe@fb.com>2016-10-26 07:49:27 -0600
commit94d7dea448fae6cbb83395323c1d2fd7f19dc388 (patch)
tree45662f72c66596b223f1ea5218dfbd8380eea2b5 /block/blk-flush.c
parent423221d1745b53656db896bd34646d09d620c759 (diff)
downloadlinux-0-day-94d7dea448fae6cbb83395323c1d2fd7f19dc388.tar.gz
block: flush: fix IO hang in case of flood fua req
This patch fixes one issue reported by Kent, which can be triggered in bcachefs over sata disk. Actually it is a generic issue in block flush vs. blk-tag. Cc: Christoph Hellwig <hch@infradead.org> Reported-by: Kent Overstreet <kent.overstreet@gmail.com> Signed-off-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-flush.c')
-rw-r--r--block/blk-flush.c28
1 files changed, 28 insertions, 0 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 6a14b68..3c882cb 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -343,6 +343,34 @@ static void flush_data_end_io(struct request *rq, int error)
struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
/*
+ * Updating q->in_flight[] here for making this tag usable
+ * early. Because in blk_queue_start_tag(),
+ * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
+ * reserve tags for sync I/O.
+ *
+ * More importantly this way can avoid the following I/O
+ * deadlock:
+ *
+ * - suppose there are 40 fua requests comming to flush queue
+ * and queue depth is 31
+ * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
+ * tag for async I/O any more
+ * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
+ * and flush_data_end_io() is called
+ * - the other rqs still can't go ahead if not updating
+ * q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
+ * are held in flush data queue and make no progress of
+ * handling post flush rq
+ * - only after the post flush rq is handled, all these rqs
+ * can be completed
+ */
+
+ elv_completed_request(q, rq);
+
+ /* for avoiding double accounting */
+ rq->cmd_flags &= ~REQ_STARTED;
+
+ /*
* After populating an empty queue, kick it to avoid stall. Read
* the comment in flush_end_io().
*/