Re: [PATCH] dm: fix iterate_device sanity check

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dm_table_supports_dax_write_cache() is remained untouched, since I'm not
sure if the semantics requires that 'any underlying device' or 'all
underlying devices' supporting dax_write_cache. At least it seems that
'any underlying device' is sufficient from the current code.

On 2/2/21 11:35 AM, Jeffle Xu wrote:
> According to the definition of dm_iterate_devices_fn:
>  * This function must iterate through each section of device used by the
>  * target until it encounters a non-zero return code, which it then returns.
>  * Returns zero if no callout returned non-zero.
> 
> For some target type (e.g., dm-stripe), one call of iterate_devices() may
> iterate multiple underlying devices internally, in which case a non-zero
> return code returned by iterate_devices_callout_fn will stop the iteration
> in advance.
> 
> Thus if we want to ensure that _all_ underlying devices support some kind of
> attribute, the iteration structure like dm_table_supports_nowait() should be
> used, while the input iterate_devices_callout_fn should handle the 'not
> support' semantics. On the opposite, the iteration structure like
> dm_table_any_device_attribute() should be used if _any_ underlying device
> supporting this attibute is sufficient. In this case, the input
> iterate_devices_callout_fn should handle the 'support' semantics.
> 
> Fixes: 545ed20e6df6 ("dm: add infrastructure for DAX support")
> Fixes: c3c4555edd10 ("dm table: clear add_random unless all devices have it set")
> Fixes: 4693c9668fdc ("dm table: propagate non rotational flag")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
> ---
>  drivers/md/dm-table.c | 84 ++++++++++++++++++++++---------------------
>  drivers/md/dm.c       |  2 +-
>  drivers/md/dm.h       |  2 +-
>  3 files changed, 46 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 4acf2342f7ad..53dcbf75eda9 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -820,24 +820,24 @@ void dm_table_set_type(struct dm_table *t, enum dm_queue_mode type)
>  EXPORT_SYMBOL_GPL(dm_table_set_type);
>  
>  /* validate the dax capability of the target device span */
> -int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
> +int device_not_dax_capable(struct dm_target *ti, struct dm_dev *dev,
>  			sector_t start, sector_t len, void *data)
>  {
>  	int blocksize = *(int *) data, id;
>  	bool rc;
>  
>  	id = dax_read_lock();
> -	rc = dax_supported(dev->dax_dev, dev->bdev, blocksize, start, len);
> +	rc = !dax_supported(dev->dax_dev, dev->bdev, blocksize, start, len);
>  	dax_read_unlock(id);
>  
>  	return rc;
>  }
>  
>  /* Check devices support synchronous DAX */
> -static int device_dax_synchronous(struct dm_target *ti, struct dm_dev *dev,
> +static int device_not_dax_synchronous_capable(struct dm_target *ti, struct dm_dev *dev,
>  				  sector_t start, sector_t len, void *data)
>  {
> -	return dev->dax_dev && dax_synchronous(dev->dax_dev);
> +	return !dev->dax_dev || !dax_synchronous(dev->dax_dev);
>  }
>  
>  bool dm_table_supports_dax(struct dm_table *t,
> @@ -854,7 +854,7 @@ bool dm_table_supports_dax(struct dm_table *t,
>  			return false;
>  
>  		if (!ti->type->iterate_devices ||
> -		    !ti->type->iterate_devices(ti, iterate_fn, blocksize))
> +		    ti->type->iterate_devices(ti, iterate_fn, blocksize))
>  			return false;
>  	}
>  
> @@ -925,7 +925,7 @@ static int dm_table_determine_type(struct dm_table *t)
>  verify_bio_based:
>  		/* We must use this table as bio-based */
>  		t->type = DM_TYPE_BIO_BASED;
> -		if (dm_table_supports_dax(t, device_supports_dax, &page_size) ||
> +		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;
>  		}
> @@ -1595,12 +1595,12 @@ static int dm_table_supports_dax_write_cache(struct dm_table *t)
>  	return false;
>  }
>  
> -static int device_is_nonrot(struct dm_target *ti, struct dm_dev *dev,
> +static int device_is_rot(struct dm_target *ti, struct dm_dev *dev,
>  			    sector_t start, sector_t len, void *data)
>  {
>  	struct request_queue *q = bdev_get_queue(dev->bdev);
>  
> -	return q && blk_queue_nonrot(q);
> +	return q && !blk_queue_nonrot(q);
>  }
>  
>  static int device_is_not_random(struct dm_target *ti, struct dm_dev *dev,
> @@ -1611,8 +1611,8 @@ static int device_is_not_random(struct dm_target *ti, struct dm_dev *dev,
>  	return q && !blk_queue_add_random(q);
>  }
>  
> -static bool dm_table_all_devices_attribute(struct dm_table *t,
> -					   iterate_devices_callout_fn func)
> +static bool dm_table_any_device_attribute(struct dm_table *t,
> +					  iterate_devices_callout_fn func)
>  {
>  	struct dm_target *ti;
>  	unsigned i;
> @@ -1620,12 +1620,12 @@ static bool dm_table_all_devices_attribute(struct dm_table *t,
>  	for (i = 0; i < dm_table_get_num_targets(t); i++) {
>  		ti = dm_table_get_target(t, i);
>  
> -		if (!ti->type->iterate_devices ||
> -		    !ti->type->iterate_devices(ti, func, NULL))
> -			return false;
> +		if (ti->type->iterate_devices &&
> +		    ti->type->iterate_devices(ti, func, NULL))
> +			return true;
>  	}
>  
> -	return true;
> +	return false;
>  }
>  
>  static int device_not_write_same_capable(struct dm_target *ti, struct dm_dev *dev,
> @@ -1780,26 +1780,25 @@ static int device_requires_stable_pages(struct dm_target *ti,
>  }
>  
>  /*
> - * If any underlying device requires stable pages, a table must require
> - * them as well.  Only targets that support iterate_devices are considered:
> - * don't want error, zero, etc to require stable pages.
> + * type->iterate_devices() should be called when the sanity check needs to
> + * iterate and check all underlying data devices. iterate_devices() will
> + * iterate all underlying data devices until it encounters a non-zero return
> + * code, returned by whether the input iterate_devices_callout_fn, or
> + * iterate_devices() itself internally.
> + *
> + * For some target type (e.g., dm-stripe), one call of iterate_devices() may
> + * iterate multiple underlying devices internally, in which case a non-zero
> + * return code returned by iterate_devices_callout_fn will stop the iteration
> + * in advance.
> + *
> + * Thus if we want to ensure that _all_ underlying devices support some kind of
> + * attribute, the iteration structure like dm_table_supports_nowait() should be
> + * used, while the input iterate_devices_callout_fn should handle the 'not
> + * support' semantics. On the opposite, the iteration structure like
> + * dm_table_any_device_attribute() should be used if _any_ underlying device
> + * supporting this attibute is sufficient. In this case, the input
> + * iterate_devices_callout_fn should handle the 'support' semantics.
>   */
> -static bool dm_table_requires_stable_pages(struct dm_table *t)
> -{
> -	struct dm_target *ti;
> -	unsigned i;
> -
> -	for (i = 0; i < dm_table_get_num_targets(t); i++) {
> -		ti = dm_table_get_target(t, i);
> -
> -		if (ti->type->iterate_devices &&
> -		    ti->type->iterate_devices(ti, device_requires_stable_pages, NULL))
> -			return true;
> -	}
> -
> -	return false;
> -}
> -
>  void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  			       struct queue_limits *limits)
>  {
> @@ -1837,9 +1836,9 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  	}
>  	blk_queue_write_cache(q, wc, fua);
>  
> -	if (dm_table_supports_dax(t, device_supports_dax, &page_size)) {
> +	if (dm_table_supports_dax(t, device_not_dax_capable, &page_size)) {
>  		blk_queue_flag_set(QUEUE_FLAG_DAX, q);
> -		if (dm_table_supports_dax(t, device_dax_synchronous, NULL))
> +		if (dm_table_supports_dax(t, device_not_dax_synchronous_capable, NULL))
>  			set_dax_synchronous(t->md->dax_dev);
>  	}
>  	else
> @@ -1849,10 +1848,10 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  		dax_write_cache(t->md->dax_dev, true);
>  
>  	/* Ensure that all underlying devices are non-rotational. */
> -	if (dm_table_all_devices_attribute(t, device_is_nonrot))
> -		blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
> -	else
> +	if (dm_table_any_device_attribute(t, device_is_rot))
>  		blk_queue_flag_clear(QUEUE_FLAG_NONROT, q);
> +	else
> +		blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
>  
>  	if (!dm_table_supports_write_same(t))
>  		q->limits.max_write_same_sectors = 0;
> @@ -1864,8 +1863,11 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  	/*
>  	 * Some devices don't use blk_integrity but still want stable pages
>  	 * because they do their own checksumming.
> +	 * If any underlying device requires stable pages, a table must require
> +	 * them as well.  Only targets that support iterate_devices are considered:
> +	 * don't want error, zero, etc to require stable pages.
>  	 */
> -	if (dm_table_requires_stable_pages(t))
> +	if (dm_table_any_device_attribute(t, device_requires_stable_pages))
>  		blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, q);
>  	else
>  		blk_queue_flag_clear(QUEUE_FLAG_STABLE_WRITES, q);
> @@ -1876,8 +1878,10 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  	 * Clear QUEUE_FLAG_ADD_RANDOM if any underlying device does not
>  	 * have it set.
>  	 */
> -	if (blk_queue_add_random(q) && dm_table_all_devices_attribute(t, device_is_not_random))
> +	if (dm_table_any_device_attribute(t, device_is_not_random))
>  		blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, q);
> +	else
> +		blk_queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q);
>  
>  	/*
>  	 * For a zoned target, the number of zones should be updated for the
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 7bac564f3faa..8a3d73efb9dd 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1128,7 +1128,7 @@ static bool dm_dax_supported(struct dax_device *dax_dev, struct block_device *bd
>  	if (!map)
>  		goto out;
>  
> -	ret = dm_table_supports_dax(map, device_supports_dax, &blocksize);
> +	ret = dm_table_supports_dax(map, device_not_dax_capable, &blocksize);
>  
>  out:
>  	dm_put_live_table(md, srcu_idx);
> diff --git a/drivers/md/dm.h b/drivers/md/dm.h
> index fffe1e289c53..b441ad772c18 100644
> --- a/drivers/md/dm.h
> +++ b/drivers/md/dm.h
> @@ -73,7 +73,7 @@ void dm_table_free_md_mempools(struct dm_table *t);
>  struct dm_md_mempools *dm_table_get_md_mempools(struct dm_table *t);
>  bool dm_table_supports_dax(struct dm_table *t, iterate_devices_callout_fn fn,
>  			   int *blocksize);
> -int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
> +int device_not_dax_capable(struct dm_target *ti, struct dm_dev *dev,
>  			   sector_t start, sector_t len, void *data);
>  
>  void dm_lock_md_type(struct mapped_device *md);
> 

-- 
Thanks,
Jeffle

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