From: Peter Zijlstra <peterz@infradead.org>
To: John Stultz <jstultz@google.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>, Hui Su <sh_def@163.com>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Zhidao Su <soolaugust@gmail.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/1] sched/proxy_exec: detect cycles in proxy walks
Date: Tue, 22 Sep 2026 09:18:16 +0200 [thread overview]
Message-ID: <20260922071816.GT4121339@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <CANDhNCqKYjO=0mFM1aidHyAWaRirD2zO4_HqH=qB+0x-Uhk9PQ@mail.gmail.com>
On Mon, Sep 21, 2026 at 11:06:52PM -0700, John Stultz wrote:
> > So if we are eventually planning on returning -EDEADLK to userspace
> > (context: https://lore.kernel.org/lkml/20260917153649.GK4121339@noisy.programming.kicks-ass.net/)
> > do we care where the chain starts or can we return -EDEADLK anywhere
> > in the chain?
>
> So returning EDEADLK to userland seems like a new feature to me, as I
> don't believe existing futexes (which can still have dependency cycles
> or just ABA style usage) currently do this.
git grep -e DEADLK -e DEADLOCK kernel/{futex,locking}
We definitely return -EDEADLK for PI futexes and rt_mutex. And given the
whole proxy thing hard relies on the block graph being acyclic, it
seems rather mandatory we enforce this before exposing it to userspace.
next prev parent reply other threads:[~2026-09-22 7:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-14 16:54 [RFC PATCH 0/1] sched/proxy_exec: detect cycles without persistent walk state Hui Su
2026-09-14 16:54 ` [RFC PATCH 1/1] sched/proxy_exec: detect cycles in proxy walks Hui Su
2026-09-22 5:26 ` John Stultz
2026-09-22 5:48 ` K Prateek Nayak
2026-09-22 6:06 ` John Stultz
2026-09-22 7:18 ` Peter Zijlstra [this message]
2026-09-19 15:51 ` [RFC PATCH 0/1] sched/proxy_exec: detect cycles without persistent walk state Hui Su
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