> On Jul 12, 2023, at 7:34 AM, Chengming Zhou <chengming.zhou@xxxxxxxxx> wrote: > > 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 for the suggestion. No change, unfortunately. > 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); -- Chuck Lever
