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

[Dan Williams <dan.j.williams@intel.com>]

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@efficios.com>
> Cc: Alasdair Kergon <agk@redhat.com>
> Cc: Mike Snitzer <snitzer@kernel.org>
> Cc: Mikulas Patocka <mpatocka@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Vishal Verma <vishal.l.verma@intel.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: linux-arch@vger.kernel.org
> Cc: linux-cxl@vger.kernel.org
> Cc: linux-fsdevel@vger.kernel.org
> Cc: linux-mm@kvack.org
> Cc: linux-xfs@vger.kernel.org
> Cc: dm-devel@lists.linux.dev
> Cc: nvdimm@lists.linux.dev
> ---
>  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.