Re: [PATCH v4 02/12] nvdimm/pmem: Treat alloc_dax() -EOPNOTSUPP failure as non-fatal

[Mathieu Desnoyers]

On 2024-02-08 16:32, Dan Williams wrote:
> Mathieu Desnoyers wrote:
> > In preparation for checking whether the architecture has data cache
> > aliasing within alloc_dax(), modify the error handling of nvdimm/pmem
> > pmem_attach_disk() to treat alloc_dax() -EOPNOTSUPP failure as non-fatal.
> >
> > For the transition, consider that alloc_dax() returning NULL is the
> > same as returning -EOPNOTSUPP.
> >
> > Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> > Cc: Alasdair Kergon <agk@xxxxxxxxxx>
> > Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> > Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> > Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > Cc: Arnd Bergmann <arnd@xxxxxxxx>
> > Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> > Cc: linux-arch@xxxxxxxxxxxxxxx
> > Cc: linux-cxl@xxxxxxxxxxxxxxx
> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> > Cc: linux-mm@xxxxxxxxx
> > Cc: linux-xfs@xxxxxxxxxxxxxxx
> > Cc: dm-devel@xxxxxxxxxxxxxxx
> > Cc: nvdimm@xxxxxxxxxxxxxxx
> > ---
> >   drivers/nvdimm/pmem.c | 26 ++++++++++++++------------
> >   1 file changed, 14 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> > index 9fe358090720..f1d9f5c6dbac 100644
> > --- a/drivers/nvdimm/pmem.c
> > +++ b/drivers/nvdimm/pmem.c
> > @@ -558,19 +558,21 @@ static int pmem_attach_disk(struct device *dev,
> >   	disk->bb = &pmem->bb;
> >   
> >   	dax_dev = alloc_dax(pmem, &pmem_dax_ops);
> > -	if (IS_ERR(dax_dev)) {
> > -		rc = PTR_ERR(dax_dev);
> > -		goto out;
> > +	if (IS_ERR_OR_NULL(dax_dev)) {
>
> alloc_dax() should never return NULL. I.e. the lead in before this patch
> should fix this misunderstanding:
>
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index b463502b16e1..df2d52b8a245 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -86,11 +86,7 @@ static inline void *dax_holder(struct dax_device *dax_dev)
>   static inline struct dax_device *alloc_dax(void *private,
>                  const struct dax_operations *ops)
>   {
> -       /*
> -        * Callers should check IS_ENABLED(CONFIG_DAX) to know if this
> -        * NULL is an error or expected.
> -        */
> -       return NULL;
> +       return ERR_PTR(-EOPNOTSUPP);
>   }
>   static inline void put_dax(struct dax_device *dax_dev)
>   {
>
> > +		rc = IS_ERR(dax_dev) ? PTR_ERR(dax_dev) : -EOPNOTSUPP;
>
> Then this ternary can be replaced with just a check of which PTR_ERR()
> value is being returned.

As you noted, I've introduced this as cleanups in later patches. I don't
mind folding these into their respective per-driver commits and moving
the alloc_dax() hunk earlier in the series.

Thanks,

Mathieu


--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com