linux-kernel - Re: [PATCH 2/2] debugfs: Remove broken no-mount mode

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Message-ID: <0101019adbfd6b56-c13ab9c4-a0dd-483c-a6fd-a6ea0d110604-000000@us-west-2.amazonses.com>
Date: Mon, 1 Dec 2025 22:16:49 +0000
From: Aaron Thompson <dev@...ont.org>
To: Mark Brown <broonie@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, Jonathan Corbet <corbet@....net>, 
	Andrew Morton <akpm@...ux-foundation.org>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Aishwarya.TCV@....com
Subject: Re: [PATCH 2/2] debugfs: Remove broken no-mount mode

On 12/1/25 09:15, Mark Brown wrote:
> On Thu, Nov 20, 2025 at 10:26:33AM +0000, Aaron Thompson wrote:
> 
>> debugfs access modes were added in Linux 5.10 (Dec 2020) [1], but the
>> no-mount mode has behaved effectively the same as the off mode since
>> Linux 5.12 (Apr 2021) [2]. The only difference is the specific error
>> code returned by the debugfs_create_* functions, which is -ENOENT in
>> no-mount mode and -EPERM in off mode.
> 
> I'm seeing regressions in -next in a lot of testing stuff which bisect
> to this patch.  I've got a test that looks at the deferred probe list to
> see if it's empty, and the mm split_huge_page_test which uses a debugfs
> file called split_huge_pages.  Neither of these mount debugfs for
> themselves, they just assume it'll be there - it looks like that's not
> happening any more but I didn't investigate properly.
> 
> I don't immediately see what's getting confused, DEBUG_FS_ALLOW_ALL is
> the default and not overridden by anything in any defconfig so
> debugfs_enabled still ought to be being set, but I didn't actually try
> to debug this yet.
> 
> Sample bisect:
> 
> git bisect start
> # status: waiting for both good and bad commits
> ...
> # bad: [f278809475f6835b56de78b28dc2cc0c7e2c20a4] debugfs: Remove broken no-mount mode
> git bisect bad f278809475f6835b56de78b28dc2cc0c7e2c20a4
> # first bad commit: [f278809475f6835b56de78b28dc2cc0c7e2c20a4] debugfs: Remove broken no-mount mode

I am terribly sorry, this was a sloppy mistake on my part. The 
IS_ENABLED() check is missing the CONFIG_ prefix. The fix patch is attached.

Greg, should I send a v2 of the patch series, or a separate patch with 
just the fix? Or something else? Again, sorry for the trouble.

-- Aaron

View attachment "debugfs-fix-is-enabled-check.patch" of type "text/x-patch" (681 bytes)