linux-kernel - Re: [PATCH 1/8] signal: Make SIGKILL during coredumps an explicit special case

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Date:   Fri, 14 Jan 2022 18:12:48 -0600
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Olivier Langlois <olivier@...llion01.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "<linux-arch@...r.kernel.org>" <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Alexey Gladkov <legion@...nel.org>,
        Kyle Huey <me@...ehuey.com>, Oleg Nesterov <oleg@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: Re: [PATCH 1/8] signal: Make SIGKILL during coredumps an explicit
 special case

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Tue, Jan 11, 2022 at 10:51 AM Eric W. Biederman
> <ebiederm@...ssion.com> wrote:
>>
>> +       while ((n == -ERESTARTSYS) && test_thread_flag(TIF_NOTIFY_SIGNAL)) {
>> +               tracehook_notify_signal();
>> +               n = __kernel_write(file, addr, nr, &pos);
>> +       }
>
> This reads horribly wrongly to me.
>
> That "tracehook_notify_signal()" thing *has* to be renamed before we
> have anything like this that otherwise looks like "this will just loop
> forever".
>
> I'm pretty sure we've discussed that "tracehook" thing before - the
> whole header file is misnamed, and most of the functions in theer are
> too.
>
> As an ugly alternative, open-code it, so that it's clear that "yup,
> that clears the TIF_NOTIFY_SIGNAL flag".

A cleaner alternative looks like to modify the pipe code to use
wake_up_XXX instead of wake_up_interruptible_XXX and then have code
that does pipe_write_killable instead of pipe_write_interruptible.

There is also a question of how all of this should interact with the
freezer, as I think changing from interruptible to killable means that
the coredumps became unfreezable.

I am busily simmering this on my back burner and I hope I can come up
with something sensible.

Eric