Hi Alexander! Apologies for the long delay on this follow-up.. Comments below. On Fri, 2013-09-20 at 17:19 +0200, Alexander Gordeev wrote: > On Thu, Aug 15, 2013 at 07:19:29PM -0700, Nicholas A. Bellinger wrote: > > Ok, here's a bit better idea of what is going on now.. > > > > The problem is that blkdev_issue_flush() -> blk_mq_make_request() -> > > __blk_mq_alloc_request() allocates the first tag, which calls > > blk_insert_flush() -> blk_flush_complete_seq() -> blk_flush_kick() -> > > mq_flush_work() -> blk_mq_alloc_request() to allocate a second tag for > > the struct request that actually gets dispatched into scsi-mq as a > > SYCHRONIZE_CACHE command.. > > > > I'm not exactly sure why this double tag usage of struct request is > > occurring, but AFAICT it does happen for every flush, and is not > > specific to the blkdev_issue_flush() codepath.. I'm sure that Jens can > > fill us in on that bit. ;) > > I also played with the double tag using a reserved tag (below). > > While it fixes 'fdisk /dev/sda' issue when trying to 'mount /dev/sda1 /mnt' > what appears to be a call to bio->bi_end_io() from the free'd bio hits in. > > Not sure if I should pursue the root cause until the whole double-tag > thingy is confirmed. > > Jens? > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 6fc1df3..81794dc 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -874,14 +874,14 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio) > hctx = q->mq_ops->map_queue(q, ctx->cpu); > > trace_block_getrq(q, bio, rw); > - rq = __blk_mq_alloc_request(hctx, GFP_ATOMIC, false); > + rq = __blk_mq_alloc_request(hctx, GFP_ATOMIC, is_flush_fua); > if (likely(rq)) > blk_mq_rq_ctx_init(ctx, rq, rw); > else { > blk_mq_put_ctx(ctx); > trace_block_sleeprq(q, bio, rw); > rq = blk_mq_alloc_request_pinned(q, rw, __GFP_WAIT|GFP_ATOMIC, > - false); > + is_flush_fua); > ctx = rq->mq_ctx; > hctx = q->mq_ops->map_queue(q, ctx->cpu); > } So this is what I ended up doing as well, and does address the specific bug with queue_depth=1. > @@ -1317,6 +1317,9 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_reg *reg, > reg->queue_depth = BLK_MQ_MAX_DEPTH; > } > > + reg->queue_depth++; > + reg->reserved_tags++; > + > ctx = alloc_percpu(struct blk_mq_ctx); > if (!ctx) > return ERR_PTR(-ENOMEM); > I was actually setting this within scsi_mq_alloc_queue(), but given that the queue_depth=1 issue is independent of scsi-mq, this does make more sense. Also, these extra increments should probably happen only when the passed queue_depth == 1 && reserved_tags == 0. Other than that minor nit. Reviewed-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html