linux-kernel - Re: [PATCH v5 1/8] dax: alloc_dax() return ERR_PTR(-EOPNOTSUPP) for CONFIG

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Date: Tue, 13 Feb 2024 07:32:26 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Dan Williams <dan.j.williams@...el.com>, Arnd Bergmann <arnd@...db.de>,
	Dave Chinner <david@...morbit.com>, 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
Subject: Re: [PATCH v5 1/8] dax: alloc_dax() return ERR_PTR(-EOPNOTSUPP) for
 CONFIG_DAX=n

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.

Thanks,

Lukas