Re: dm: Call proper helper to determine dax support

[Mike Snitzer <snitzer@redhat.com>]

On Wed, Sep 16 2020 at 11:14am -0400,
Jan Kara <jack@suse.cz> wrote:

> DM was calling generic_fsdax_supported() to determine whether a device
> referenced in the DM table supports DAX. However this is a helper for "leaf" device drivers so that
> they don't have to duplicate common generic checks. High level code
> should call dax_supported() helper which that calls into appropriate
> helper for the particular device. This problem manifested itself as
> kernel messages:
> 
> dm-3: error: dax access failed (-95)
> 
> when lvm2-testsuite run in cases where a DM device was stacked on top of
> another DM device.
> 
> Fixes: 7bf7eac8d648 ("dax: Arrange for dax_supported check to span multiple devices")
> Tested-by: Adrian Huang <ahuang12@lenovo.com>
> Signed-off-by: Jan Kara <jack@suse.cz>

Looked good:

Acked-by: Mike Snitzer <snitzer@redhat.com>

This fix should Cc stable@ right?

> ---
>  drivers/dax/super.c   |  4 ++++
>  drivers/md/dm-table.c |  3 +--
>  include/linux/dax.h   | 11 +++++++++--
>  3 files changed, 14 insertions(+), 4 deletions(-)
> 
> This patch should go in together with Adrian's
> https://lore.kernel.org/linux-nvdimm/20200916133923.31-1-adrianhuang0701@gmail.com

Sure, but there really isn't a dependency right?

Dan, will you be picking these up to send to Linux for 5.9-rc?

Thanks,
Mike


> 
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index e5767c83ea23..b6284c5cae0a 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -325,11 +325,15 @@ EXPORT_SYMBOL_GPL(dax_direct_access);
>  bool dax_supported(struct dax_device *dax_dev, struct block_device *bdev,
>  		int blocksize, sector_t start, sector_t len)
>  {
> +	if (!dax_dev)
> +		return false;
> +
>  	if (!dax_alive(dax_dev))
>  		return false;
>  
>  	return dax_dev->ops->dax_supported(dax_dev, bdev, blocksize, start, len);
>  }
> +EXPORT_SYMBOL_GPL(dax_supported);
>  
>  size_t dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
>  		size_t bytes, struct iov_iter *i)
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 5edc3079e7c1..bed1ff0744ec 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -862,8 +862,7 @@ int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
>  {
>  	int blocksize = *(int *) data;
>  
> -	return generic_fsdax_supported(dev->dax_dev, dev->bdev, blocksize,
> -				       start, len);
> +	return dax_supported(dev->dax_dev, dev->bdev, blocksize, start, len);
>  }
>  
>  /* Check devices support synchronous DAX */
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 6904d4e0b2e0..9f916326814a 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -130,6 +130,8 @@ static inline bool generic_fsdax_supported(struct dax_device *dax_dev,
>  	return __generic_fsdax_supported(dax_dev, bdev, blocksize, start,
>  			sectors);
>  }
> +bool dax_supported(struct dax_device *dax_dev, struct block_device *bdev,
> +		int blocksize, sector_t start, sector_t len);
>  
>  static inline void fs_put_dax(struct dax_device *dax_dev)
>  {
> @@ -157,6 +159,13 @@ static inline bool generic_fsdax_supported(struct dax_device *dax_dev,
>  	return false;
>  }
>  
> +static inline bool dax_supported(struct dax_device *dax_dev,
> +		struct block_device *bdev, int blocksize, sector_t start,
> +		sector_t len)
> +{
> +	return false;
> +}
> +
>  static inline void fs_put_dax(struct dax_device *dax_dev)
>  {
>  }
> @@ -195,8 +204,6 @@ bool dax_alive(struct dax_device *dax_dev);
>  void *dax_get_private(struct dax_device *dax_dev);
>  long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
>  		void **kaddr, pfn_t *pfn);
> -bool dax_supported(struct dax_device *dax_dev, struct block_device *bdev,
> -		int blocksize, sector_t start, sector_t len);
>  size_t dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
>  		size_t bytes, struct iov_iter *i);
>  size_t dax_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff, void *addr,
> -- 
> 2.16.4
> 
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