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From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: "Josh Poimboeuf" <jpoimboe@redhat.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Vito Caputo" <vcaputo@pengaru.com>,
	"Jann Horn" <jannh@google.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>, "Jens Axboe" <axboe@kernel.dk>,
	"Stefan Metzmacher" <metze@samba.org>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Lai Jiangshan" <laijs@linux.alibaba.com>,
	"Christian Brauner" <christian.brauner@ubuntu.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Kenta.Tada@sony.com" <Kenta.Tada@sony.com>,
	"Daniel Bristot de Oliveira" <bristot@redhat.com>,
	"Michael Weiß" <michael.weiss@aisec.fraunhofer.de>,
	"Anand K Mistry" <amistry@google.com>,
	"Alexey Gladkov" <legion@kernel.org>,
	"Michal Hocko" <mhocko@suse.com>, "Helge Deller" <deller@gmx.de>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Andrea Righi" <andrea.righi@canonical.com>,
	"Ohhoon Kwon" <ohoono.kwon@samsung.com>,
	"Kalesh Singh" <kaleshsingh@google.com>,
	"YiFei Zhu" <yifeifz2@illinois.edu>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"Qi Zheng" <zhengqi.arch@bytedance.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] proc: Disable /proc/$pid/wchan
Date: Wed, 29 Sep 2021 21:40:26 +0200	[thread overview]
Message-ID: <20210929194026.GA4323@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <202109291152.681444A135@keescook>

On Wed, Sep 29, 2021 at 11:54:55AM -0700, Kees Cook wrote:

> > > > > > It's supposed to show where a blocked task is blocked; the "wait
> > > > > > channel".

> Since I think we're considering get_wchan() to be slow-path, can we just
> lock the runqueue and use arch_stack_walk_reliable()?

Funny thing, when a task is blocked it isn't on the runqueue :-)

So if all we want to do is capture a blocked task and fail otherwise we
don't need the rq->lock at all.

Something like:

	unsigned long ip = 0;

	raw_spin_lock_irq(&p->pi_lock);
	state = READ_ONCE(p->__state);
	smp_rmb(); /* see try_to_wake_up() */
	if (state == TASK_RUNNING || state == TASK_WAKING || p->on_rq)
		goto unlock;

	ip = /* do actual stack walk on a blocked task */
unlock:
	raw_spin_unlock_irq(&p->pi_lock);

	return ip;


Should get us there.


  parent reply	other threads:[~2021-09-29 19:46 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-23 23:31 [PATCH] proc: Disable /proc/$pid/wchan Kees Cook
2021-09-23 23:38 ` Kees Cook
2021-09-24 13:31   ` Peter Zijlstra
2021-09-23 23:49 ` Vito Caputo
2021-09-24  0:08   ` Jann Horn
2021-09-24  0:22     ` Vito Caputo
2021-09-24  1:16       ` Kees Cook
2021-09-24  1:34         ` Vito Caputo
2021-09-24  1:42           ` Kees Cook
2021-09-24 13:54         ` Mark Rutland
2021-09-24 14:26           ` Kees Cook
2021-09-27  9:03             ` Mark Rutland
2021-09-27 18:07               ` Kees Cook
2021-09-27 20:50                 ` Josh Poimboeuf
2021-09-29 18:54                   ` Kees Cook
2021-09-29 19:00                     ` Mark Brown
2021-09-29 19:26                       ` Kees Cook
2021-09-29 19:40                     ` Peter Zijlstra [this message]
2021-09-29 21:10                       ` Josh Poimboeuf
2021-09-27  9:16           ` David Laight
2021-09-29  8:48           ` Peter Zijlstra
2021-09-24  2:13 ` Andrew Morton
2021-09-24  6:04   ` Kees Cook
2021-09-24 13:29 ` Peter Zijlstra
2021-09-30 18:05 ` Stephen Brennan
2021-09-30 18:12   ` Kees Cook

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