Previously, if a fs request which was being drained failed and got
requeued, blk_do_ordered() didn't allow it to be reissued, which
causes queue stall. This patch makes blk_do_ordered() use the
sequence of each request to determine whether a request can be issued
or not. This fixes the bug and simplifies code.
Signed-off-by: Tejun Heo <[email protected]>
--
Jens, this fix is not very urgent. The bug is not likely to be
triggered easily. I think pushing this to -mm first would be better.
Thanks.
Signed-off-by: Tejun Heo <[email protected]>
diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index ec27dda..701808e 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -494,7 +494,7 @@ static inline struct request *start_orde
int blk_do_ordered(request_queue_t *q, struct request **rqp)
{
- struct request *rq = *rqp, *allowed_rq;
+ struct request *rq = *rqp;
int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
if (!q->ordseq) {
@@ -518,32 +518,26 @@ int blk_do_ordered(request_queue_t *q, s
}
}
+ /*
+ * Ordered sequence in progress
+ */
+
+ /* Special requests are not subject to ordering rules. */
+ if (!blk_fs_request(rq) &&
+ rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
+ return 1;
+
if (q->ordered & QUEUE_ORDERED_TAG) {
+ /* Ordered by tag. Blocking the next barrier is enough. */
if (is_barrier && rq != &q->bar_rq)
*rqp = NULL;
- return 1;
+ } else {
+ /* Ordered by draining. Wait for turn. */
+ WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
+ if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
+ *rqp = NULL;
}
- switch (blk_ordered_cur_seq(q)) {
- case QUEUE_ORDSEQ_PREFLUSH:
- allowed_rq = &q->pre_flush_rq;
- break;
- case QUEUE_ORDSEQ_BAR:
- allowed_rq = &q->bar_rq;
- break;
- case QUEUE_ORDSEQ_POSTFLUSH:
- allowed_rq = &q->post_flush_rq;
- break;
- default:
- allowed_rq = NULL;
- break;
- }
-
- if (rq != allowed_rq &&
- (blk_fs_request(rq) || rq == &q->pre_flush_rq ||
- rq == &q->post_flush_rq))
- *rqp = NULL;
-
return 1;
}
-
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