From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: rjw@rjwysocki.net, mingo@kernel.org, vincent.guittot@linaro.org,
dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de,
Will Deacon <will@kernel.org>, Tejun Heo <tj@kernel.org>,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH] freezer,sched: Rewrite core freezer logic
Date: Mon, 14 Jun 2021 17:42:47 +0200 [thread overview]
Message-ID: <20210614154246.GB13677@redhat.com> (raw)
In-Reply-To: <YMMijNqaLDbS3sIv@hirez.programming.kicks-ass.net>
Hi Peter, sorry for delay,
On 06/11, Peter Zijlstra wrote:
>
> +/* Recursion relies on tail-call optimization to not blow away the stack */
> +static bool __frozen(struct task_struct *p)
> +{
> + if (p->state == TASK_FROZEN)
> + return true;
> +
> + /*
> + * If stuck in TRACED, and the ptracer is FROZEN, we're frozen too.
> + */
> + if (task_is_traced(p))
> + return frozen(rcu_dereference(p->parent));
Why does it use frozen(), not __frozen() ?
This looks racy, p->parent can resume this task and then enter
__refrigerator().
Plus this task can be SIGKILL'ed even if it is traced.
> + /*
> + * If stuck in STOPPED and the parent is FROZEN, we're frozen too.
> + */
> + if (task_is_stopped(p))
> + return frozen(rcu_dereference(p->real_parent));
(you could use ->parent in this case too and unify this check with the
"traced" case above)
I don't understand. How this connects to ->parent or ->real_parent?
SIGCONT can come from anywhere and wake this stopped task up?
I guess you do this to avoid freezable_schedule() in ptrace/signal_stop,
and we can't use TASK_STOPPED|TASK_FREEZABLE, it should not run after
thaw()... But see above, we can't rely on __frozen(parent).
Oleg.
next prev parent reply other threads:[~2021-06-14 15:42 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-11 8:45 [PATCH] freezer,sched: Rewrite core freezer logic Peter Zijlstra
2021-06-11 8:46 ` Peter Zijlstra
2021-06-11 13:58 ` Rafael J. Wysocki
2021-06-14 15:42 ` Oleg Nesterov [this message]
2021-06-14 16:12 ` Peter Zijlstra
2021-06-14 16:54 ` Oleg Nesterov
2021-06-14 18:38 ` Peter Zijlstra
2021-06-15 15:45 ` Oleg Nesterov
2021-06-15 21:35 ` Peter Zijlstra
2021-06-15 21:50 ` Peter Zijlstra
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