linux-kernel - Re: Commit *pidfd: prevent creation of pidfds for kthreads* causes `Failed to remount '/' read-only: Device or resource busy`

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Message-ID: <17001e93-7baf-428b-b979-e6fb8330cb84@molgen.mpg.de>
Date: Tue, 20 Aug 2024 07:31:11 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Thorsten Leemhuis <regressions@...mhuis.info>
Cc: Christian Brauner <brauner@...nel.org>, linux-kernel@...r.kernel.org,
 regressions@...ts.linux.dev
Subject: Re: Commit *pidfd: prevent creation of pidfds for kthreads* causes
 `Failed to remount '/' read-only: Device or resource busy`

Dear Thorsten,


Am 20.08.24 um 07:03 schrieb Thorsten Leemhuis:
> On 19.08.24 23:02, Paul Menzel wrote:
>> #regzbot introduced: 3b5bbe798b24
>>
>> Commit 3b5bbe798b24 (pidfd: prevent creation of pidfds for kthreads)
>> causes a regression. On the Dell XPS 13 9360 with Debian sid/unstable
>> and *systemd* 256.5-1, systemd is not able to unmount the root partition
>> (LUKS encrypted) anymore.
> 
> Hi Paul! Thx for the report. FWIW, a revert to fix this is already
> queued as 780d60bac21ebe ("Revert "pidfd: prevent creation of pidfds for
> kthreads"") [next-20240820 (pending-fixes)] after Eric reported similar
> problems recently:
> 
> https://lore.kernel.org/all/20240819-staudamm-rederei-cb7092f54e76@brauner/

Thank you for digging this up. I thought I search for the commit hash in 
lore.kernel.org, but maybe I hit the wrong button *locate inbox*.

Anyway, reverting the patch on top of master also fixes the issue for 
me. Maybe Linus can take it directly, as more people are going to run 
into this.


Kind regards,

Paul