On Thu, Sep 17, 2020 at 10:30:03PM -0700, Dan Williams wrote:
> From: Jan Kara <jack@xxxxxxx>
>
> 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.
Is there somewhere where it is documented which of:
bdev_dax_supported, generic_fsdax_supported, and dax_supported
one is supposed to use for a given circumstance?
I guess the last two can test a given range w/ blocksize; the first one
only does blocksize; and the middle one also checks with whatever fs
might be mounted? <shrug>
(I ask because it took me a while to figure out how to revert correctly
the brokenness in rc3-5 that broke my nightly dax fstesting.)
--D
>
> Fixes: 7bf7eac8d648 ("dax: Arrange for dax_supported check to span multiple devices")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Tested-by: Adrian Huang <ahuang12@xxxxxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> Acked-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
> Changes since v1 [1]:
> - Add missing dax_read_lock() around dax_supported()
>
> [1]: http://lore.kernel.org/r/20200916151445.450-1-jack@xxxxxxx
>
> drivers/dax/super.c | 4 ++++
> drivers/md/dm-table.c | 10 +++++++---
> include/linux/dax.h | 11 +++++++++--
> 3 files changed, 20 insertions(+), 5 deletions(-)
>
> 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..229f461e7def 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -860,10 +860,14 @@ EXPORT_SYMBOL_GPL(dm_table_set_type);
> int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
> sector_t start, sector_t len, void *data)
> {
> - int blocksize = *(int *) data;
> + int blocksize = *(int *) data, id;
> + bool rc;
>
> - return generic_fsdax_supported(dev->dax_dev, dev->bdev, blocksize,
> - start, len);
> + id = dax_read_lock();
> + rc = dax_supported(dev->dax_dev, dev->bdev, blocksize, start, len);
> + dax_read_unlock(id);
> +
> + return rc;
> }
>
> /* 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,
>
> --
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> https://www.redhat.com/mailman/listinfo/dm-devel
>
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