From: Alois Wohlschlager <alwoju@gmx.de>
To: Christian Brauner <brauner@kernel.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Alexey Gladkov <legion@kernel.org>, Jens Axboe <axboe@kernel.dk>,
David Hildenbrand <david@redhat.com>,
Rolf Eike Beer <eb@emlix.com>,
Ran Xiaokai <ran.xiaokai@zte.com.cn>,
Matthew Bobrowski <repnop@google.com>, Jan Kara <jack@suse.cz>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] pid: Allow creation of pidfds to threads
Date: Fri, 01 Apr 2022 11:00:27 +0200 [thread overview]
Message-ID: <5392366.5i5WIIk9Ns@genesis> (raw)
In-Reply-To: <20220401070942.odjbuc5wecfayyok@wittgenstein>
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Hello Christian,
> We originally blocked this because it is not as easy as simply allowing
> pidfds to be created for non-thread-group leaders.
> For a start, pidfd_poll() currently doens't work if pidfd_task() isn't a
> thread-group leader
I did notice the hang there, that's why my patch changes pidfd_poll to return
error on tasks which are not thread-group leaders. IIRC, waiting on specific
threads is not supported by Linux at all, so I don't see a problem with not
supporting it here either.
> and you'll just hang for CLONE_PIDFD | CLONE_THREAD.
No, CLONE_PIDFD | CLONE_THREAD behavior is unchanged, it will still fail with
EINVAL. I actually confirmed this by double-checking right now.
> So at least that needs to be adapated as well and there's likely a bunch
> of other corner-cases I'm forgetting about.
I'd be happy to hear about other corner-cases so I can fix them.
> Do you have a concrete use-case you want this for?
My use-case is basically making pidfd_getfd actually useful for its intended
purpose: there is a seccomp_unotify-based supervisor that wants to obtain a
file descriptor from its guest. This currently does not work if the action to
be forwarded to the supervisor is performed in a secondary thread, since there
is no way to obtain the required pidfd.
> Christian
Alois
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next prev parent reply other threads:[~2022-04-01 9:01 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-31 19:02 [PATCH] pid: Allow creation of pidfds to threads Alois Wohlschlager
2022-04-01 7:09 ` Christian Brauner
2022-04-01 9:00 ` Alois Wohlschlager [this message]
2022-04-01 9:42 ` Christian Brauner
2022-04-13 4:46 ` Matthew Bobrowski
2022-04-14 8:11 ` Alois Wohlschlager
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