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Message-ID: <457bde90-5ce7-4c60-9268-e5980ddf6cc0@efficios.com>
Date: Tue, 13 Feb 2024 15:07:38 -0500
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Subject: Re: [PATCH v5 1/8] dax: alloc_dax() return ERR_PTR(-EOPNOTSUPP) for
 CONFIG_DAX=n
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To: Dan Williams <dan.j.williams@intel.com>, Lukas Wunner <lukas@wunner.de>
Cc: Arnd Bergmann <arnd@arndb.de>, Dave Chinner <david@fromorbit.com>,
 linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
 Linus Torvalds <torvalds@linux-foundation.org>,
 Vishal Verma <vishal.l.verma@intel.com>, Dave Jiang <dave.jiang@intel.com>,
 Matthew Wilcox <willy@infradead.org>, Russell King <linux@armlinux.org.uk>,
 linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org,
 linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
 linux-xfs@vger.kernel.org, dm-devel@lists.linux.dev, nvdimm@lists.linux.dev,
 linux-s390@vger.kernel.org
References: <20240212163101.19614-1-mathieu.desnoyers@efficios.com>
 <20240212163101.19614-2-mathieu.desnoyers@efficios.com>
 <20240213063226.GA4740@wunner.de>
 <65cbbdfe19172_29b129476@dwillia2-mobl3.amr.corp.intel.com.notmuch>
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
In-Reply-To: <65cbbdfe19172_29b129476@dwillia2-mobl3.amr.corp.intel.com.notmuch>
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On 2024-02-13 14:07, Dan Williams wrote:
> Lukas Wunner wrote:
>> On Mon, Feb 12, 2024 at 11:30:54AM -0500, Mathieu Desnoyers wrote:
>>> Change the return value from NULL to PTR_ERR(-EOPNOTSUPP) for
>>> CONFIG_DAX=n to be consistent with the fact that CONFIG_DAX=y
>>> never returns NULL.
>>
>> All the callers of alloc_dax() only check for IS_ERR().
>>
>> Doesn't this result in a change of behavior in all the callers?
>> Previously they'd ignore the NULL return value and continue,
>> now they'll error out.
>>
>> Given that, seems dangerous to add a Fixes tag with a v4.0 commit
>> and thus risk regressing all stable kernels.
> 
> Oh, good catch, yes that Fixes tag should be:
> 
> 4e4ced93794a dax: Move mandatory ->zero_page_range() check in alloc_dax()
> 
> ...as that was the one that updated the alloc_dax() calling convention
> without fixing up the CONFIG_DAX=n case.
> 
> This is a pre-requisite for restoring DAX operation on ARM32.

I'll change the Fixes tag in this commit to:

Fixes: 4e4ced93794a ("dax: Move mandatory ->zero_page_range() check in alloc_dax()")

for v6.

Thanks,

Mathieu

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