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

[Jan Kara]

 On Mon 21-09-20 11:23:07, Naresh Kamboju wrote:
> On Fri, 18 Sep 2020 at 11:18, Dan Williams <dan.j.williams@xxxxxxxxx> 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.
> >
> > 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);
> 
> 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 <naresh.kamboju@xxxxxxxxxx>
> 
> 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
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR