linux-kernel - Re: [PATCH v2 2/2] getrusage: use sig->stats_lock rather than lock_task

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Message-Id: <20240122155723.149081552c9a9e122b1f783b@linux-foundation.org>
Date: Mon, 22 Jan 2024 15:57:23 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Dylan Hatch
 <dylanbhatch@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] getrusage: use sig->stats_lock rather than
 lock_task_sighand()

On Mon, 22 Jan 2024 16:50:53 +0100 Oleg Nesterov <oleg@...hat.com> wrote:

> lock_task_sighand() can trigger a hard lockup. If NR_CPUS threads call
> getrusage() at the same time and the process has NR_THREADS, spin_lock_irq
> will spin with irqs disabled O(NR_CPUS * NR_THREADS) time.

It would be super interesting to see Dylan's original report.

Is it possible for carefully-crafted unprivileged userspace to
deliberately trigger this?