linux-kernel - Re: [PATCH] time: Remove CONFIG_TIMER

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Date:   Wed, 8 Feb 2017 10:09:39 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kees Cook <keescook@...omium.org>, Xing Gao <xgao01@...il.wm.edu>,
        Jessica Frazelle <me@...sfraz.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jonathan Corbet <corbet@....net>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Nicolas Iooss <nicolas.iooss_linux@....org>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Richard Cochran <richardcochran@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Michal Marek <mmarek@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Olof Johansson <olof@...om.net>, Shuah Khan <shuah@...nel.org>,
        linux-doc@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] time: Remove CONFIG_TIMER_STATS

On Wed, Feb 8, 2017 at 2:24 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Tue, 7 Feb 2017, John Stultz wrote:
>> On Tue, Feb 7, 2017 at 3:40 PM, Kees Cook <keescook@...omium.org> wrote:
>> > Currently CONFIG_TIMER_STATS exposes process information across namespaces:
>> >
>> > kernel/time/timer_list.c print_timer():
>> >
>> >         SEQ_printf(m, ", %s/%d", tmp, timer->start_pid);
>> >
>> > /proc/timer_list:
>> >
>> >  #11: <0000000000000000>, hrtimer_wakeup, S:01, do_nanosleep, cron/2570
>> >
>> > Given that the tracer can give the same information, this patch entirely
>> > removes CONFIG_TIMER_STATS.
>> >
>> > Suggested-by: Thomas Gleixner <tglx@...utronix.de>
>> > Signed-off-by: Kees Cook <keescook@...omium.org>
>>
>> I don't have an issue with this, but I worry this would break some
>> tooling out there. Should it be marked as deprecated first?
>>
>> Or maybe just pulling the band-aid off is the best way?
>
> I think we should just kill it.
>
> No tools can really rely on the behaviour of that file because it depends
> on CONFIG_TIMER_STATS and the information available there is just a random
> snapshot of queued timers at a given point of time, which is in no way
> usefull.

Fair enough.

Acked-by: John Stultz <john.stultz@...aro.org>