[v2] dm: Call proper helper to determine dax support

Commit Message

Dan Williams Sept. 18, 2020, 5:30 a.m. UTC

From: Jan Kara <[e-mail]>

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")
Cc: <[e-mail]>
Tested-by: Adrian Huang <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>
Acked-by: Mike Snitzer <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>
---
Changes since v1 [1]:
- Add missing dax_read_lock() around dax_supported()

[1]: http://lore.kernel.org/r/[e-mail]

 drivers/dax/super.c   |    4 ++++
 drivers/md/dm-table.c |   10 +++++++---
 include/linux/dax.h   |   11 +++++++++--
 3 files changed, 20 insertions(+), 5 deletions(-)


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Comments

Darrick J. Wong Sept. 18, 2020, 3:30 p.m. UTC | #1

On Thu, Sep 17, 2020 at 10:30:03PM -0700, Dan Williams wrote:
> From: Jan Kara <[e-mail]>
> 
> 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: <[e-mail]>
> Tested-by: Adrian Huang <[e-mail]>
> Signed-off-by: Jan Kara <[e-mail]>
> Acked-by: Mike Snitzer <[e-mail]>
> Signed-off-by: Dan Williams <[e-mail]>
> ---
> Changes since v1 [1]:
> - Add missing dax_read_lock() around dax_supported()
> 
> [1]: http://lore.kernel.org/r/[e-mail]
> 
>  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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Dan Williams Sept. 18, 2020, 4:54 p.m. UTC | #2

On Fri, Sep 18, 2020 at 8:31 AM Darrick J. Wong <[e-mail]> wrote:
>
> On Thu, Sep 17, 2020 at 10:30:03PM -0700, Dan Williams wrote:
> > From: Jan Kara <[e-mail]>
> >
> > 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?

generic_fsdax_supported should be private to device drivers populating
their dax_operations. I think it deserves a rename at this point.
dax_supported() knows how to route through multiple layers of stacked
block-devices to ask the "is dax supported" question at each level.

> 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.)

Again, apologies for that.

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Naresh Kamboju Sept. 21, 2020, 5:53 a.m. UTC | #3

On Fri, 18 Sep 2020 at 11:18, Dan Williams <[e-mail]> wrote:
>
> From: Jan Kara <[e-mail]>
>
> 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")
> Cc: <[e-mail]>
> Tested-by: Adrian Huang <[e-mail]>
> Signed-off-by: Jan Kara <[e-mail]>
> Acked-by: Mike Snitzer <[e-mail]>
> Signed-off-by: Dan Williams <[e-mail]>
> ---
> Changes since v1 [1]:
> - Add missing dax_read_lock() around dax_supported()
>
> [1]: http://lore.kernel.org/r/[e-mail]
>
>  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);

arm build error while building with allmodconfig.

../drivers/dax/super.c:325:6: error: redefinition of ‘dax_supported’
  325 | bool dax_supported(struct dax_device *dax_dev, struct
block_device *bdev,
      |      ^~~~~~~~~~~~~
In file included from ../drivers/dax/super.c:16:
../include/linux/dax.h:162:20: note: previous definition of
‘dax_supported’ was here
  162 | static inline bool dax_supported(struct dax_device *dax_dev,
      |                    ^~~~~~~~~~~~~
make[3]: *** [../scripts/Makefile.build:283: drivers/dax/super.o] Error 1

Reported-by: Naresh Kamboju <[e-mail]>

Ref:
https://builds.tuxbuild.com/IO690jFQDp0qP9zFuWBqpA/build.log


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Jan Kara Sept. 21, 2020, 9:58 a.m. UTC | #4

On Mon 21-09-20 11:23:07, Naresh Kamboju wrote:
> On Fri, 18 Sep 2020 at 11:18, Dan Williams <[e-mail]> wrote:
> >
> > From: Jan Kara <[e-mail]>
> >
> > 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")
> > Cc: <[e-mail]>
> > Tested-by: Adrian Huang <[e-mail]>
> > Signed-off-by: Jan Kara <[e-mail]>
> > Acked-by: Mike Snitzer <[e-mail]>
> > Signed-off-by: Dan Williams <[e-mail]>
> > ---
> > Changes since v1 [1]:
> > - Add missing dax_read_lock() around dax_supported()
> >
> > [1]: http://lore.kernel.org/r/[e-mail]
> >
> >  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);
> 
> arm build error while building with allmodconfig.
> 
> ../drivers/dax/super.c:325:6: error: redefinition of ‘dax_supported’
>   325 | bool dax_supported(struct dax_device *dax_dev, struct
> block_device *bdev,
>       |      ^~~~~~~~~~~~~
> In file included from ../drivers/dax/super.c:16:
> ../include/linux/dax.h:162:20: note: previous definition of
> ‘dax_supported’ was here
>   162 | static inline bool dax_supported(struct dax_device *dax_dev,
>       |                    ^~~~~~~~~~~~~
> make[3]: *** [../scripts/Makefile.build:283: drivers/dax/super.o] Error 1
> 
> Reported-by: Naresh Kamboju <[e-mail]>
> 
> Ref:
> https://builds.tuxbuild.com/IO690jFQDp0qP9zFuWBqpA/build.log

Thanks for report! Attached patch should fix the build (at least I've
tested it with CONFIG_DAX && CONFIG_FS_DAX, CONFIG_DAX && !CONFIG_FS_DAX,
and !CONFIG_DAX cases). Dan can you please merge the fix?

								Honza

Patch

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,