linux-kernel - Re: [PATCH v2 12/12] sched,signal,ptrace: Rework TASK_TRACED, TASK

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Message-ID: <Ym+v9VAf71oOlDLF@linutronix.de>
Date:   Mon, 2 May 2022 12:18:29 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, rjw@...ysocki.net,
        Oleg Nesterov <oleg@...hat.com>, mingo@...nel.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, mgorman@...e.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>, linux-ia64@...r.kernel.org
Subject: Re: [PATCH v2 12/12] sched,signal,ptrace: Rework TASK_TRACED,
 TASK_STOPPED state

On 2022-04-29 16:48:37 [-0500], Eric W. Biederman wrote:

Needs
 From: Peter Zijlstra (Intel) <peterz@...radead.org>

at the top.

> Currently ptrace_stop() / do_signal_stop() rely on the special states
> TASK_TRACED and TASK_STOPPED resp. to keep unique state. That is, this
> state exists only in task->__state and nowhere else.
> 
> There's two spots of bother with this:
> 
>  - PREEMPT_RT has task->saved_state which complicates matters,
>    meaning task_is_{traced,stopped}() needs to check an additional
>    variable.
> 
>  - An alternative freezer implementation that itself relies on a
>    special TASK state would loose TASK_TRACED/TASK_STOPPED and will
>    result in misbehaviour.
> 
> As such, add additional state to task->jobctl to track this state
> outside of task->__state.
> 
> NOTE: this doesn't actually fix anything yet, just adds extra state.
> 
> --EWB
>   * didn't add a unnecessary newline in signal.h
>   * Update t->jobctl in signal_wake_up and ptrace_signal_wake_up
>     instead of in signal_wake_up_state.  This prevents the clearing
>     of TASK_STOPPED and TASK_TRACED from getting lost.
>   * Added warnings if JOBCTL_STOPPED or JOBCTL_TRACED are not cleared
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: https://lkml.kernel.org/r/20220421150654.757693825@infradead.org
> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>

Sebastian