On 2023/7/11 20:01, Christoph Hellwig wrote: > On Mon, Jul 10, 2023 at 05:40:42PM +0000, Chuck Lever III wrote: >>> blk_rq_init_flush(rq); >>> - rq->flush.seq |= REQ_FSEQ_POSTFLUSH; >>> + rq->flush.seq |= REQ_FSEQ_PREFLUSH; >>> spin_lock_irq(&fq->mq_flush_lock); >>> list_move_tail(&rq->flush.list, &fq->flush_data_in_flight); >>> spin_unlock_irq(&fq->mq_flush_lock); >> >> Thanks for the quick response. No change. > > I'm a bit lost and still can't reprodce. Below is a patch with the > only behavior differences I can find. It has two "#if 1" blocks, > which I'll need to bisect to to find out which made it work (if any, > but I hope so). Hello, I tried today to reproduce, but can't unfortunately. Could you please also try the fix patch [1] from Ross Lagerwall that fixes IO hung problem of plug recursive flush? (Since the main difference is that post-flush requests now can go into plug.) [1] https://lore.kernel.org/all/20230711160434.248868-1-ross.lagerwall@xxxxxxxxxx/ Thanks! > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 5504719b970d59..67364e607f2d1d 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -2927,6 +2927,7 @@ void blk_mq_submit_bio(struct bio *bio) > struct request_queue *q = bdev_get_queue(bio->bi_bdev); > struct blk_plug *plug = blk_mq_plug(bio); > const int is_sync = op_is_sync(bio->bi_opf); > + bool is_flush = op_is_flush(bio->bi_opf); > struct blk_mq_hw_ctx *hctx; > struct request *rq; > unsigned int nr_segs = 1; > @@ -2967,16 +2968,23 @@ void blk_mq_submit_bio(struct bio *bio) > return; > } > > - if (op_is_flush(bio->bi_opf) && blk_insert_flush(rq)) > - return; > - > - if (plug) { > - blk_add_rq_to_plug(plug, rq); > - return; > +#if 1 /* Variant 1, the plug is holding us back */ > + if (op_is_flush(bio->bi_opf)) { > + if (blk_insert_flush(rq)) > + return; > + } else { > + if (plug) { > + blk_add_rq_to_plug(plug, rq); > + return; > + } > } > +#endif > > hctx = rq->mq_hctx; > if ((rq->rq_flags & RQF_USE_SCHED) || > +#if 1 /* Variant 2 (unlikely), blk_mq_try_issue_directly causes problems */ > + is_flush || > +#endif > (hctx->dispatch_busy && (q->nr_hw_queues == 1 || !is_sync))) { > blk_mq_insert_request(rq, 0); > blk_mq_run_hw_queue(hctx, true);
