From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: block: add a bi_error field to struct bio Date: Thu, 4 Jun 2015 11:31:07 -0400 Message-ID: <20150604153106.GA31567@redhat.com> References: <1433338959-24808-1-git-send-email-hch@lst.de> <1433338959-24808-2-git-send-email-hch@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1433338959-24808-2-git-send-email-hch@lst.de> Sender: linux-raid-owner@vger.kernel.org To: Christoph Hellwig Cc: Jens Axboe , linux-raid@vger.kernel.org, dm-devel@redhat.com, linux-btrfs@vger.kernel.org List-Id: linux-raid.ids On Wed, Jun 03 2015 at 9:42P -0400, Christoph Hellwig wrote: > Currently we have two different ways to signal an I/O error on a BIO: > > (1) by clearing the BIO_UPTODATE flag > (2) by returning a Linux errno value to the bi_end_io callback > > The first one has the drawback of only communicating a single possible > error (-EIO), and the second one has the drawback of not beeing persistent > when bios are queued up, and are not passed along from child to parent > bio in the ever more popular chaining scenario. Having both mechanisms > available has the additional drawback of utterly confusing driver authors > and introducing bugs where various I/O submitters only deal with one of > them, and the others have to add boilerplate code to deal with both kinds > of error returns. > > So add a new bi_error field to store an errno value directly in struct > bio and remove the existing mechanisms to clean all this up. > > Signed-off-by: Christoph Hellwig This patch _really_ concerns me because just in DM alone I found you took liberties that you shouldn't have and created a regression. First issue is a real bug (your proposed dm-io.c:dmio_complete change missed that dm-io uses error_bits and not traditional error code like expected) the other issue being you added extra branching that isn't needed and made review more tedious (dm.c:clone_endio). I'll defer to others to check their respective areas of expertise but my experience with this review should really underscore the need for more eyes on this patch. That said, I do appreciate your effort on cleaning this up! For DM, please add Signed-off-by: Mike Snitzer once you've folded in this patch, thanks! diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index 86dbbc7..d2fc49f 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -545,7 +545,8 @@ static void dmio_complete(unsigned long error, void *context) { struct dm_buffer *b = context; - b->bio.bi_end_io(&b->bio, error ? -EIO : 0); + b->bio.bi_error = error ? -EIO : 0; + b->bio.bi_end_io(&b->bio); } static void use_dmio(struct dm_buffer *b, int rw, sector_t block, diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 767bce9..85a7c3d 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -954,25 +954,22 @@ static void disable_write_same(struct mapped_device *md) limits->max_write_same_sectors = 0; } -static void clone_endio(struct bio *bio, int error) +static void clone_endio(struct bio *bio) { - int r = error; + int r = bio->bi_error; struct dm_target_io *tio = container_of(bio, struct dm_target_io, clone); struct dm_io *io = tio->io; struct mapped_device *md = tio->io->md; dm_endio_fn endio = tio->ti->type->end_io; - if (!bio_flagged(bio, BIO_UPTODATE) && !error) - error = -EIO; - if (endio) { - r = endio(tio->ti, bio, error); + r = endio(tio->ti, bio, bio->bi_error); if (r < 0 || r == DM_ENDIO_REQUEUE) /* * error and requeue request are handled * in dec_pending(). */ - error = r; + ; else if (r == DM_ENDIO_INCOMPLETE) /* The target will handle the io */ return; @@ -987,7 +984,7 @@ static void clone_endio(struct bio *bio, int error) disable_write_same(md); free_tio(md, tio); - dec_pending(io, error); + dec_pending(io, r); } static struct dm_rq_target_io *tio_from_request(struct request *rq)