From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: lk 3.17-rc4 blk_mq large write problems Date: Wed, 10 Sep 2014 08:41:44 -0700 Message-ID: <20140910154144.GA22296@infradead.org> References: <540FCB96.8000606@interlog.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from bombadil.infradead.org ([198.137.202.9]:51919 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751094AbaIJPlp (ORCPT ); Wed, 10 Sep 2014 11:41:45 -0400 Content-Disposition: inline In-Reply-To: <540FCB96.8000606@interlog.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Douglas Gilbert Cc: SCSI development list , Jens Axboe While it might not help with a blown stack, can you give the patch below a try? I tries to solve a problem where the timeout handler hits before we've fully set up a command. While I'd like to understand the root cause of why we're hitting it as well, I'd also really to fix that race. It would also be good to get a gdb listing of the exact area in scsi_times_out listed in the oops. --- From: Christoph Hellwig Subject: blk-mq: call blk_mq_start_request from ->queue_rq When we call blk_mq_start_request from the core blk-mq code before calling into ->queue_rq there is a racy window where the timeout handler can hit before we've fully set up the driver specific part of the command. Move the call to blk_mq_start_request into the driver so the driver can start the request only once it is fully set up. Signed-off-by: Christoph Hellwig diff --git a/block/blk-mq.c b/block/blk-mq.c index 5189cb1..db9990b 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -374,7 +374,7 @@ void blk_mq_complete_request(struct request *rq) } EXPORT_SYMBOL(blk_mq_complete_request); -static void blk_mq_start_request(struct request *rq, bool last) +void blk_mq_start_request(struct request *rq) { struct request_queue *q = rq->q; @@ -405,29 +405,18 @@ static void blk_mq_start_request(struct request *rq, bool last) */ rq->nr_phys_segments++; } - - /* - * Flag the last request in the series so that drivers know when IO - * should be kicked off, if they don't do it on a per-request basis. - * - * Note: the flag isn't the only condition drivers should do kick off. - * If drive is busy, the last request might not have the bit set. - */ - if (last) - rq->cmd_flags |= REQ_END; } +EXPORT_SYMBOL(blk_mq_start_request); static void __blk_mq_requeue_request(struct request *rq) { struct request_queue *q = rq->q; trace_block_rq_requeue(q, rq); - clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags); - - rq->cmd_flags &= ~REQ_END; - - if (q->dma_drain_size && blk_rq_bytes(rq)) - rq->nr_phys_segments--; + if (test_and_clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags)) { + if (q->dma_drain_size && blk_rq_bytes(rq)) + rq->nr_phys_segments--; + } } void blk_mq_requeue_request(struct request *rq) @@ -735,9 +724,7 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) rq = list_first_entry(&rq_list, struct request, queuelist); list_del_init(&rq->queuelist); - blk_mq_start_request(rq, list_empty(&rq_list)); - - ret = q->mq_ops->queue_rq(hctx, rq); + ret = q->mq_ops->queue_rq(hctx, rq, list_empty(&rq_list)); switch (ret) { case BLK_MQ_RQ_QUEUE_OK: queued++; @@ -1177,14 +1164,13 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio) int ret; blk_mq_bio_to_request(rq, bio); - blk_mq_start_request(rq, true); /* * For OK queue, we are done. For error, kill it. Any other * error (busy), just add it to our list as we previously * would have done */ - ret = q->mq_ops->queue_rq(data.hctx, rq); + ret = q->mq_ops->queue_rq(data.hctx, rq, true); if (ret == BLK_MQ_RQ_QUEUE_OK) goto done; else { diff --git a/drivers/block/mtip32xx/mtip32xx.c b/drivers/block/mtip32xx/mtip32xx.c index db1e956..9b0127a 100644 --- a/drivers/block/mtip32xx/mtip32xx.c +++ b/drivers/block/mtip32xx/mtip32xx.c @@ -3775,13 +3775,16 @@ static bool mtip_check_unal_depth(struct blk_mq_hw_ctx *hctx, return false; } -static int mtip_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *rq) +static int mtip_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *rq, + bool last) { int ret; if (unlikely(mtip_check_unal_depth(hctx, rq))) return BLK_MQ_RQ_QUEUE_BUSY; + blk_mq_start_request(rq); + ret = mtip_submit_request(hctx, rq); if (likely(!ret)) return BLK_MQ_RQ_QUEUE_OK; diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c index a3b042c..d098adfbb 100644 --- a/drivers/block/null_blk.c +++ b/drivers/block/null_blk.c @@ -313,10 +313,13 @@ static void null_request_fn(struct request_queue *q) } } -static int null_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *rq) +static int null_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *rq, + bool last) { struct nullb_cmd *cmd = blk_mq_rq_to_pdu(rq); + blk_mq_start_request(rq); + cmd->rq = rq; cmd->nq = hctx->driver_data; diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 0a58140..4b08906 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c @@ -164,14 +164,14 @@ static void virtblk_done(struct virtqueue *vq) spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags); } -static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req) +static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req, + bool last) { struct virtio_blk *vblk = hctx->queue->queuedata; struct virtblk_req *vbr = blk_mq_rq_to_pdu(req); unsigned long flags; unsigned int num; int qid = hctx->queue_num; - const bool last = (req->cmd_flags & REQ_END) != 0; int err; bool notify = false; @@ -213,6 +213,8 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req) vbr->out_hdr.type |= VIRTIO_BLK_T_IN; } + blk_mq_start_request(req); + spin_lock_irqsave(&vblk->vqs[qid].lock, flags); err = __virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg, num); if (err) { diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 9c44392..dd6e912 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1856,7 +1856,8 @@ static void scsi_mq_done(struct scsi_cmnd *cmd) blk_mq_complete_request(cmd->request); } -static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req) +static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req, + bool last) { struct request_queue *q = req->q; struct scsi_device *sdev = q->queuedata; @@ -1890,6 +1891,8 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req) scsi_init_cmd_errh(cmd); cmd->scsi_done = scsi_mq_done; + blk_mq_start_request(req); + reason = scsi_dispatch_cmd(cmd); if (reason) { scsi_set_blocked(cmd, reason); diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index eb726b9..aed92d5 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -77,7 +77,7 @@ struct blk_mq_tag_set { struct list_head tag_list; }; -typedef int (queue_rq_fn)(struct blk_mq_hw_ctx *, struct request *); +typedef int (queue_rq_fn)(struct blk_mq_hw_ctx *, struct request *, bool); typedef struct blk_mq_hw_ctx *(map_queue_fn)(struct request_queue *, const int); typedef int (init_hctx_fn)(struct blk_mq_hw_ctx *, void *, unsigned int); typedef void (exit_hctx_fn)(struct blk_mq_hw_ctx *, unsigned int); @@ -160,6 +160,7 @@ struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag); struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *, const int ctx_index); struct blk_mq_hw_ctx *blk_mq_alloc_single_hw_queue(struct blk_mq_tag_set *, unsigned int, int); +void blk_mq_start_request(struct request *rq); void blk_mq_end_io(struct request *rq, int error); void __blk_mq_end_io(struct request *rq, int error); diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index 66c2167..bb7d664 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -188,7 +188,6 @@ enum rq_flag_bits { __REQ_MIXED_MERGE, /* merge of different types, fail separately */ __REQ_KERNEL, /* direct IO to kernel pages */ __REQ_PM, /* runtime pm request */ - __REQ_END, /* last of chain of requests */ __REQ_HASHED, /* on IO scheduler merge hash */ __REQ_MQ_INFLIGHT, /* track inflight for MQ */ __REQ_NR_BITS, /* stops here */ @@ -242,7 +241,6 @@ enum rq_flag_bits { #define REQ_SECURE (1ULL << __REQ_SECURE) #define REQ_KERNEL (1ULL << __REQ_KERNEL) #define REQ_PM (1ULL << __REQ_PM) -#define REQ_END (1ULL << __REQ_END) #define REQ_HASHED (1ULL << __REQ_HASHED) #define REQ_MQ_INFLIGHT (1ULL << __REQ_MQ_INFLIGHT)