Re: [PATCH 5.4 26/34] dm verity: set DM_TARGET_IMMUTABLE feature flag

[Guenter Roeck <linux@xxxxxxxxxxxx>]

On 6/15/22 13:02, Mike Snitzer wrote:
> On Wed, Jun 15 2022 at  1:50P -0400,
> Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> > On 6/15/22 08:29, Mike Snitzer wrote:
> > > On Wed, Jun 15 2022 at 10:36P -0400,
> > > Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > >
> > > > On Mon, Jun 13, 2022 at 11:13:21AM +0200, Greg KH wrote:
> > > > > On Fri, Jun 10, 2022 at 11:11:00AM -0400, Mike Snitzer wrote:
> > > > > > On Fri, Jun 10 2022 at  1:15P -0400,
> > > > > > Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > > > > >
> > > > > > > On Fri, Jun 10, 2022 at 04:22:00AM +0000, Oleksandr Tymoshenko wrote:
> > > > > > > > I believe this commit introduced a regression in dm verity on systems
> > > > > > > > where data device is an NVME one. Loading table fails with the
> > > > > > > > following diagnostics:
> > > > > > > >
> > > > > > > > device-mapper: table: table load rejected: including non-request-stackable devices
> > > > > > > >
> > > > > > > > The same kernel works with the same data drive on the SCSI interface.
> > > > > > > > NVME-backed dm verity works with just this commit reverted.
> > > > > > > >
> > > > > > > > I believe the presence of the immutable partition is used as an indicator
> > > > > > > > of special case NVME configuration and if the data device's name starts
> > > > > > > > with "nvme" the code tries to switch the target type to
> > > > > > > > DM_TYPE_NVME_BIO_BASED (drivers/md/dm-table.c lines 1003-1010).
> > > > > > > >
> > > > > > > > The special NVME optimization case was removed in
> > > > > > > > 5.10 by commit 9c37de297f6590937f95a28bec1b7ac68a38618f, so only 5.4 is
> > > > > > > > affected.
> > > > > > >
> > > > > > > Why wouldn't 4.9, 4.14, and 4.19 also be affected here?  Should I also
> > > > > > > just queue up 9c37de297f65 ("dm: remove special-casing of bio-based
> > > > > > > immutable singleton target on NVMe") to those older kernels?  If so,
> > > > > > > have you tested this and verified that it worked?
> > > > > >
> > > > > > Sorry for the unforeseen stable@ troubles here!
> > > > > >
> > > > > > In general we'd be fine to apply commit 9c37de297f65 but to do it
> > > > > > properly would require also making sure commits that remove
> > > > > > "DM_TYPE_NVME_BIO_BASED", like 8d47e65948dd ("dm mpath: remove
> > > > > > unnecessary NVMe branching in favor of scsi_dh checks") are applied --
> > > > > > basically any lingering references to DM_TYPE_NVME_BIO_BASED need to
> > > > > > be removed.
> > > > > >
> > > > > > The commit header for 8d47e65948dd documents what
> > > > > > DM_TYPE_NVME_BIO_BASED was used for.. it was dm-mpath specific and
> > > > > > "nvme" mode really never got used by any userspace that I'm aware of.
> > > > > >
> > > > > > Sadly I currently don't have the time to do this backport for all N
> > > > > > stable kernels... :(
> > > > > >
> > > > > > But if that backport gets out of control: A simpler, albeit stable@
> > > > > > unicorn, way to resolve this is to simply revert 9c37de297f65 and make
> > > >
> > > > 9c37de297f65 can not be reverted in 5.4 and older because it isn't there,
> > > > and trying to apply it results in conflicts which at least I can not
> > > > resolve.
> > > >
> > > > > > it so that DM-mpath and DM core just used bio-based if "nvme" is
> > > > > > requested by dm-mpath, so also in drivers/md/dm-mpath.c e.g.:
> > > > > >
> > > > > > @@ -1091,8 +1088,6 @@ static int parse_features(struct dm_arg_set *as, struct multipath *m)
> > > > > >
> > > > > >                           if (!strcasecmp(queue_mode_name, "bio"))
> > > > > >                                   m->queue_mode = DM_TYPE_BIO_BASED;
> > > > > > 			else if (!strcasecmp(queue_mode_name, "nvme"))
> > > > > > -                               m->queue_mode = DM_TYPE_NVME_BIO_BASED;
> > > > > > +                               m->queue_mode = DM_TYPE_BIO_BASED;
> > > > > >                           else if (!strcasecmp(queue_mode_name, "rq"))
> > > > > >                                   m->queue_mode = DM_TYPE_REQUEST_BASED;
> > > > > >                           else if (!strcasecmp(queue_mode_name, "mq"))
> > > > > >
> > > > > > Mike
> > > > >
> > > > > Ok, please submit a working patch for the kernels that need it so that
> > > > > we can review and apply it to solve this regression.
> > > >
> > > > So, effectively, v5.4.y and older are broken right now for use cases
> > > > with dm on NVME drives.
> > > >
> > > > Given that the regression does affect older branches, and given that we
> > > > have to revert this patch to avoid regressions in ChromeOS, would it be
> > > > possible to revert it from v5.4.y and older until a fix is found ?
> > >
> > > I obviously would prefer to not have this false-start.
> > The false start has already happened since we had to revert the patch
> > from chromeos-5.4 and older branches.
>
> OK, well this is pretty easy to fix in general.  If there are slight
> differences across older trees they are easily resolved.  Fact that
> stable@ couldn't cope with backporting 9c37de297f65 is.. what it is.
>
> But this will fix the issue on 5.4.y:
>
> From: Mike Snitzer <snitzer@xxxxxxxxxx>
> Date: Wed, 15 Jun 2022 14:07:09 -0400
> Subject: [5.4.y PATCH] dm: remove special-casing of bio-based immutable singleton target on NVMe
>
> Commit 9c37de297f6590937f95a28bec1b7ac68a38618f upstream.
>
> There is no benefit to DM special-casing NVMe. Remove all code used to
> establish DM_TYPE_NVME_BIO_BASED.
>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>

This patch passes our tests after I removed the unused variable.

Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

Thanks a lot for the backport!

Guenter

> ---
>   drivers/md/dm-table.c         | 32 ++----------------
>   drivers/md/dm.c               | 64 +++--------------------------------
>   include/linux/device-mapper.h |  1 -
>   3 files changed, 7 insertions(+), 90 deletions(-)
>
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 06b382304d92..81bc36a43b32 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -872,8 +872,7 @@ EXPORT_SYMBOL(dm_consume_args);
>   static bool __table_type_bio_based(enum dm_queue_mode table_type)
>   {
>   	return (table_type == DM_TYPE_BIO_BASED ||
> -		table_type == DM_TYPE_DAX_BIO_BASED ||
> -		table_type == DM_TYPE_NVME_BIO_BASED);
> +		table_type == DM_TYPE_DAX_BIO_BASED);
>   }
>   
>   static bool __table_type_request_based(enum dm_queue_mode table_type)
> @@ -929,8 +928,6 @@ bool dm_table_supports_dax(struct dm_table *t,
>   	return true;
>   }
>   
> -static bool dm_table_does_not_support_partial_completion(struct dm_table *t);
> -
>   static int device_is_rq_stackable(struct dm_target *ti, struct dm_dev *dev,
>   				  sector_t start, sector_t len, void *data)
>   {
> @@ -960,7 +957,6 @@ static int dm_table_determine_type(struct dm_table *t)
>   			goto verify_bio_based;
>   		}
>   		BUG_ON(t->type == DM_TYPE_DAX_BIO_BASED);
> -		BUG_ON(t->type == DM_TYPE_NVME_BIO_BASED);
>   		goto verify_rq_based;
>   	}
>   
> @@ -999,15 +995,6 @@ static int dm_table_determine_type(struct dm_table *t)
>   		if (dm_table_supports_dax(t, device_not_dax_capable, &page_size) ||
>   		    (list_empty(devices) && live_md_type == DM_TYPE_DAX_BIO_BASED)) {
>   			t->type = DM_TYPE_DAX_BIO_BASED;
> -		} else {
> -			/* Check if upgrading to NVMe bio-based is valid or required */
> -			tgt = dm_table_get_immutable_target(t);
> -			if (tgt && !tgt->max_io_len && dm_table_does_not_support_partial_completion(t)) {
> -				t->type = DM_TYPE_NVME_BIO_BASED;
> -				goto verify_rq_based; /* must be stacked directly on NVMe (blk-mq) */
> -			} else if (list_empty(devices) && live_md_type == DM_TYPE_NVME_BIO_BASED) {
> -				t->type = DM_TYPE_NVME_BIO_BASED;
> -			}
>   		}
>   		return 0;
>   	}
> @@ -1024,8 +1011,7 @@ static int dm_table_determine_type(struct dm_table *t)
>   	 * (e.g. request completion process for partial completion.)
>   	 */
>   	if (t->num_targets > 1) {
> -		DMERR("%s DM doesn't support multiple targets",
> -		      t->type == DM_TYPE_NVME_BIO_BASED ? "nvme bio-based" : "request-based");
> +		DMERR("request-based DM doesn't support multiple targets");
>   		return -EINVAL;
>   	}
>   
> @@ -1714,20 +1700,6 @@ static int device_is_not_random(struct dm_target *ti, struct dm_dev *dev,
>   	return q && !blk_queue_add_random(q);
>   }
>   
> -static int device_is_partial_completion(struct dm_target *ti, struct dm_dev *dev,
> -					sector_t start, sector_t len, void *data)
> -{
> -	char b[BDEVNAME_SIZE];
> -
> -	/* For now, NVMe devices are the only devices of this class */
> -	return (strncmp(bdevname(dev->bdev, b), "nvme", 4) != 0);
> -}
> -
> -static bool dm_table_does_not_support_partial_completion(struct dm_table *t)
> -{
> -	return !dm_table_any_dev_attr(t, device_is_partial_completion, NULL);
> -}
> -
>   static int device_not_write_same_capable(struct dm_target *ti, struct dm_dev *dev,
>   					 sector_t start, sector_t len, void *data)
>   {
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 37b8bb4d80f0..3c45c389ded9 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1000,7 +1000,7 @@ static void clone_endio(struct bio *bio)
>   	struct mapped_device *md = tio->io->md;
>   	dm_endio_fn endio = tio->ti->type->end_io;
>   
> -	if (unlikely(error == BLK_STS_TARGET) && md->type != DM_TYPE_NVME_BIO_BASED) {
> +	if (unlikely(error == BLK_STS_TARGET)) {
>   		if (bio_op(bio) == REQ_OP_DISCARD &&
>   		    !bio->bi_disk->queue->limits.max_discard_sectors)
>   			disable_discard(md);
> @@ -1340,10 +1340,7 @@ static blk_qc_t __map_bio(struct dm_target_io *tio)
>   		/* the bio has been remapped so dispatch it */
>   		trace_block_bio_remap(clone->bi_disk->queue, clone,
>   				      bio_dev(io->orig_bio), sector);
> -		if (md->type == DM_TYPE_NVME_BIO_BASED)
> -			ret = direct_make_request(clone);
> -		else
> -			ret = generic_make_request(clone);
> +		ret = generic_make_request(clone);
>   		break;
>   	case DM_MAPIO_KILL:
>   		if (unlikely(swap_bios_limit(ti, clone))) {
> @@ -1732,51 +1729,6 @@ static blk_qc_t __split_and_process_bio(struct mapped_device *md,
>   	return ret;
>   }
>   
> -/*
> - * Optimized variant of __split_and_process_bio that leverages the
> - * fact that targets that use it do _not_ have a need to split bios.
> - */
> -static blk_qc_t __process_bio(struct mapped_device *md, struct dm_table *map,
> -			      struct bio *bio, struct dm_target *ti)
> -{
> -	struct clone_info ci;
> -	blk_qc_t ret = BLK_QC_T_NONE;
> -	int error = 0;
> -
> -	init_clone_info(&ci, md, map, bio);
> -
> -	if (bio->bi_opf & REQ_PREFLUSH) {
> -		struct bio flush_bio;
> -
> -		/*
> -		 * Use an on-stack bio for this, it's safe since we don't
> -		 * need to reference it after submit. It's just used as
> -		 * the basis for the clone(s).
> -		 */
> -		bio_init(&flush_bio, NULL, 0);
> -		flush_bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC;
> -		ci.bio = &flush_bio;
> -		ci.sector_count = 0;
> -		error = __send_empty_flush(&ci);
> -		bio_uninit(ci.bio);
> -		/* dec_pending submits any data associated with flush */
> -	} else {
> -		struct dm_target_io *tio;
> -
> -		ci.bio = bio;
> -		ci.sector_count = bio_sectors(bio);
> -		if (__process_abnormal_io(&ci, ti, &error))
> -			goto out;
> -
> -		tio = alloc_tio(&ci, ti, 0, GFP_NOIO);
> -		ret = __clone_and_map_simple_bio(&ci, tio, NULL);
> -	}
> -out:
> -	/* drop the extra reference count */
> -	dec_pending(ci.io, errno_to_blk_status(error));
> -	return ret;
> -}
> -
>   static blk_qc_t dm_process_bio(struct mapped_device *md,
>   			       struct dm_table *map, struct bio *bio)
>   {
> @@ -1807,8 +1759,6 @@ static blk_qc_t dm_process_bio(struct mapped_device *md,
>   		/* regular IO is split by __split_and_process_bio */
>   	}
>   
> -	if (dm_get_md_type(md) == DM_TYPE_NVME_BIO_BASED)
> -		return __process_bio(md, map, bio, ti);
>   	return __split_and_process_bio(md, map, bio);
>   }
>   
> @@ -2200,12 +2150,10 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
>   	if (request_based)
>   		dm_stop_queue(q);
>   
> -	if (request_based || md->type == DM_TYPE_NVME_BIO_BASED) {
> +	if (request_based) {
>   		/*
> -		 * Leverage the fact that request-based DM targets and
> -		 * NVMe bio based targets are immutable singletons
> -		 * - used to optimize both dm_request_fn and dm_mq_queue_rq;
> -		 *   and __process_bio.
> +		 * Leverage the fact that request-based DM targets are
> +		 * immutable singletons - used to optimize dm_mq_queue_rq.
>   		 */
>   		md->immutable_target = dm_table_get_immutable_target(t);
>   	}
> @@ -2334,7 +2282,6 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
>   		break;
>   	case DM_TYPE_BIO_BASED:
>   	case DM_TYPE_DAX_BIO_BASED:
> -	case DM_TYPE_NVME_BIO_BASED:
>   		dm_init_congested_fn(md);
>   		break;
>   	case DM_TYPE_NONE:
> @@ -3070,7 +3017,6 @@ struct dm_md_mempools *dm_alloc_md_mempools(struct mapped_device *md, enum dm_qu
>   	switch (type) {
>   	case DM_TYPE_BIO_BASED:
>   	case DM_TYPE_DAX_BIO_BASED:
> -	case DM_TYPE_NVME_BIO_BASED:
>   		pool_size = max(dm_get_reserved_bio_based_ios(), min_pool_size);
>   		front_pad = roundup(per_io_data_size, __alignof__(struct dm_target_io)) + offsetof(struct dm_target_io, clone);
>   		io_front_pad = roundup(front_pad,  __alignof__(struct dm_io)) + offsetof(struct dm_io, tio);
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index a53d7d2c2d95..60631f3abddb 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -28,7 +28,6 @@ enum dm_queue_mode {
>   	DM_TYPE_BIO_BASED	 = 1,
>   	DM_TYPE_REQUEST_BASED	 = 2,
>   	DM_TYPE_DAX_BIO_BASED	 = 3,
> -	DM_TYPE_NVME_BIO_BASED	 = 4,
>   };
>   
>   typedef enum { STATUSTYPE_INFO, STATUSTYPE_TABLE } status_type_t;