linux-kernel - Re: [PATCH] tick/sched: fix data races at tick_do_timer

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Message-ID: <87tv34laqq.fsf@nanos.tec.linutronix.de>
Date:   Wed, 04 Mar 2020 10:39:41 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Qian Cai <cai@....pw>, fweisbec@...il.com, mingo@...nel.org
Cc:     elver@...gle.com, linux-kernel@...r.kernel.org,
        Qian Cai <cai@....pw>, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] tick/sched: fix data races at tick_do_timer_cpu

Qian,

Qian Cai <cai@....pw> writes:
> tick_do_timer_cpu could be accessed concurrently where both plain writes
> and plain reads are not protected by a lock. Thus, it could result in
> data races. Fix them by adding pairs of READ|WRITE_ONCE(). The data
> races were reported by KCSAN,

They are reported, but are they actually a real problem?

This completely lacks analysis why these 8 places need the
READ/WRITE_ONCE() treatment at all and if so why the other 14 places
accessing tick_do_timer_cpu are safe without it.

I definitely appreciate the work done with KCSAN, but just making the
tool shut up does not cut it. 

Thanks,

        tglx