linux-kernel - Re: [PATCH v4 02/12] nvdimm/pmem: Treat alloc

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Date: Thu, 8 Feb 2024 17:07:15 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Dan Williams <dan.j.williams@...el.com>, Arnd Bergmann <arnd@...db.de>,
 Dave Chinner <david@...morbit.com>
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>,
 Matthew Wilcox <willy@...radead.org>, Russell King <linux@...linux.org.uk>,
 linux-arch@...r.kernel.org, linux-cxl@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-xfs@...r.kernel.org, dm-devel@...ts.linux.dev, nvdimm@...ts.linux.dev,
 linux-s390@...r.kernel.org, Alasdair Kergon <agk@...hat.com>,
 Mike Snitzer <snitzer@...nel.org>, Mikulas Patocka <mpatocka@...hat.com>
Subject: Re: [PATCH v4 02/12] nvdimm/pmem: Treat alloc_dax() -EOPNOTSUPP
 failure as non-fatal

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@...icios.com>
>> Cc: Alasdair Kergon <agk@...hat.com>
>> Cc: Mike Snitzer <snitzer@...nel.org>
>> Cc: Mikulas Patocka <mpatocka@...hat.com>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> Cc: Dan Williams <dan.j.williams@...el.com>
>> Cc: Vishal Verma <vishal.l.verma@...el.com>
>> Cc: Dave Jiang <dave.jiang@...el.com>
>> Cc: Matthew Wilcox <willy@...radead.org>
>> Cc: Arnd Bergmann <arnd@...db.de>
>> Cc: Russell King <linux@...linux.org.uk>
>> Cc: linux-arch@...r.kernel.org
>> Cc: linux-cxl@...r.kernel.org
>> Cc: linux-fsdevel@...r.kernel.org
>> Cc: linux-mm@...ck.org
>> Cc: linux-xfs@...r.kernel.org
>> Cc: dm-devel@...ts.linux.dev
>> Cc: nvdimm@...ts.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.

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