linux-kernel - Re: [PATCH 9/9] ptrace: Don't change _

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Message-ID: <20220428185311.GF15485@redhat.com>
Date:   Thu, 28 Apr 2022 20:53:11 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, rjw@...ysocki.net, mingo@...nel.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, mgorman@...e.de, bigeasy@...utronix.de,
        Will Deacon <will@...nel.org>, tj@...nel.org,
        linux-pm@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>,
        linux-um@...ts.infradead.org, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org, Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH 9/9] ptrace: Don't change __state

On 04/28, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> >> The bug appears when the TRACEE makes it to schedule().  Inside
> >> schedule there is a call to signal_pending_state() which notices
> >> a SIGKILL is pending and refuses to sleep.
> >
> > And I think this is fine. This doesn't really differ from the case
> > when the tracee was killed before it takes siglock.
>
> Hmm.  Maybe.

I hope ;)

> Previously we were actually guaranteed in ptrace_check_attach that after
> ptrace_freeze_traced would succeed as any pending fatal signal would
> cause ptrace_freeze_traced to fail.  Any incoming fatal signal would not
> stop schedule from sleeping.

Yes.

So let me repeat, 7/9 "ptrace: Simplify the wait_task_inactive call in
ptrace_check_attach" looks good to me (except it should use
wait_task_inactive(__TASK_TRACED)), but it should come before other
meaningfull changes and the changelog should be updated.

And then we will probably need to reconsider this wait_task_inactive()
and WARN_ON() around it, but depends on what will we finally do.

> I think in my tired mind yesterday

I got lost too ;)

> Still I would like to be able to
> let wait_task_inactive not care about the state of the process it is
> going to sleep for.

Not sure... but to be honest I didn't really pay attention to the
wait_task_inactive(match_state => 0) part...

Oleg.