Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 29 Sep 2021 10:48:53 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Vito Caputo <vcaputo@pengaru.com>,
        Jann Horn <jannh@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        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 =?iso-8859-1?Q?Wei=DF?= 
        <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>,
        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
Message-ID: <YVQodT191JGCCY/F@hirez.programming.kicks-ass.net>
References: <20210923233105.4045080-1-keescook@chromium.org>
 <20210923234917.pqrxwoq7yqnvfpwu@shells.gnugeneration.com>
 <CAG48ez0Rtv5kqHWw368Ym3GkKodPA+JETOAN+=c2KPa3opENSA@mail.gmail.com>
 <20210924002230.sijoedia65hf5bj7@shells.gnugeneration.com>
 <202109231814.FD09DBAD3@keescook>
 <20210924135424.GA33573@C02TD0UTHF1T.local>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210924135424.GA33573@C02TD0UTHF1T.local>
Precedence: bulk

On Fri, Sep 24, 2021 at 02:54:24PM +0100, Mark Rutland wrote:
> We could instead have the scheduler entrypoints snapshot their caller
> into a field in task_struct. If there are sufficiently few callers, that
> could be an inline wrapper that passes a __func__ string. Otherwise, we
> still need to symbolize.

I strongly dislike that option, we'd make the scheduler slower for
something that's typically unused.

The 3 people actually using wchan should pay the cost of obtaining the
data, not everybody all the time.