linux-kernel - Re: [PATCH v3] proc: Ensure we see the exit of each process tid exactly

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Message-ID: <87v9lkbrtu.fsf@x220.int.ebiederm.org>
Date:   Mon, 27 Apr 2020 15:23:57 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Alexey Gladkov <legion@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3] proc: Ensure we see the exit of each process tid exactly

ebiederm@...ssion.com (Eric W. Biederman) writes:
> Take a good look over the code base and see if I can see any more
> issues like was found in next_tgid and repost the core patches.

Oleg,

I am reading through kernel/ptrace.c and I am seeing a lot of:

	spin_lock(&child->sighand->siglock);

In places where I don't see anything guaranteeing the child is stopped
such as ptrace_freeze_traced.  Are all of those places safe or
do some of the need to be transformed into lock_task_sighand in
case the process is current running?

I might just be reading the code to quickly and missing what keeps the
code from executing exec and changing sighand.

Eric