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Date: Thu, 25 Jan 2024 19:25:05 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Tycho Andersen <tycho@tycho.pizza>
Cc: Christian Brauner <brauner@kernel.org>, linux-kernel@vger.kernel.org,
	linux-api@vger.kernel.org, Tycho Andersen <tandersen@netflix.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH v3 1/3] pidfd: allow pidfd_open() on non-thread-group
 leaders
Message-ID: <20240125182505.GD5513@redhat.com>
References: <20240123153452.170866-1-tycho@tycho.pizza>
 <20240123153452.170866-2-tycho@tycho.pizza>
 <20240123195608.GB9978@redhat.com>
 <ZbArN3EYRfhrNs3o@tycho.pizza>
 <20240125140830.GA5513@redhat.com>
 <20240125-tricksen-baugrube-3f78c487a23a@brauner>
 <20240125175113.GC5513@redhat.com>
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On 01/25, Tycho Andersen wrote:
>
> One of the things I don't like about PIDFD_THREAD is that it's hard to
> tell whether an arbitrary thread is a leader or not. Right now we do
> it by parsing /proc/pid/status, which shows all the stuff from
> do_task_stat() that we don't care about but which is quite expensive
> to compute. (Maybe there's a better way?)
>
> With PIDFD_THREAD we could could do it twice, once with the flag, get
> EINVAL, and then do it again. But ideally we wouldn't have to.

Too late for me, most probably I misunderstood.

If you want the PIDFD_THREAD behaviour, you can always use this flag
without any check...

Could you spell?

Oleg.