linux-kernel - Re: [GIT PULL] thread fixes v5.6-rc6

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Date:   Thu, 12 Mar 2020 17:49:34 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] thread fixes v5.6-rc6

On Wed, Mar 11, 2020 at 04:44:05PM +0100, Christian Brauner wrote:
> Hey Linus,
> 
> /* Summary */
> This contains a single fix for a regression which was introduced when we
> introduced the ability to select a specific pid at process creation time. When
> this feature is requested, the error value will be set to -EPERM after exiting
> the pid allocation loop. This caused EPERM to be returned when e.g. the init
> process/child subreaper of the pid namespace has already died where we used to
> return ENOMEM before.
> The first patch here simply fixes the regression by unconditionally setting the
> return value back to ENOMEM again once we've successfully allocated the
> requested pid number. This should be easy to backport to v5.5.
> 
> The second patch adds a comment explaining that we must keep returning ENOMEM
> since we've been doing it for a long time and have explicitly documented this
> behavior for userspace. This seemed worthwhile because we now have at least two
> separate example where people tried to change the return value to something
> other than ENOMEM (The first version of the regression fix did that too and the
> commit message links to an earlier patch that tried to do the same.).
> 
> I have a simple regression test to make sure we catch this regression in the
> future but since that introduces a whole new selftest subdir and test files
> I'll keep this for v5.7.
> 
> /* Testing */
> All patches have seen exposure in linux-next and are based on v5.6-rc1.

Hm, just noticed this was supposed to be v5.6-rc4 as can be seen from
the base commit below. Missed to update it.

> I've had a build warning reported to me for the first version of the second
> patch two days ago that tried to remove the unconditional initalization but
> that's fixed and linux-next seemed happy. The second patch is now a pure
> non-functional change.
> 
> /* Conflicts */
> At the time of creating this pr no merge conflicts were reported with anything
> that is expected to land this merge window.
> 
> The following changes since commit 98d54f81e36ba3bf92172791eba5ca5bd813989b:
> 
>   Linux 5.6-rc4 (2020-03-01 16:38:46 -0600)
> 
> are available in the Git repository at:
> 
>   git@...olite.kernel.org:pub/scm/linux/kernel/git/brauner/linux tags/for-linus-2020-03-10
> 
> for you to fetch changes up to 10dab84caf400f2f5f8b010ebb0c7c4272ec5093:
> 
>   pid: make ENOMEM return value more obvious (2020-03-09 23:40:05 +0100)
> 
> Please consider pulling these changes from the signed for-linus-2020-03-10 tag.
> 
> Thanks!
> Christian
> 
> ----------------------------------------------------------------
> for-linus-2020-03-10
> 
> ----------------------------------------------------------------
> Christian Brauner (1):
>       pid: make ENOMEM return value more obvious
> 
> Corey Minyard (1):
>       pid: Fix error return value in some cases
> 
>  kernel/pid.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>