linux-kernel - Re: BUG: KCSAN: data-race in mutex_spin_on

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Message-ID: <20201207115115.GL3040@hirez.programming.kicks-ass.net>
Date:   Mon, 7 Dec 2020 12:51:15 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     open list <linux-kernel@...r.kernel.org>,
        linux-usb@...r.kernel.org, lkft-triage@...ts.linaro.org,
        rcu@...r.kernel.org, kasan-dev <kasan-dev@...glegroups.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Marco Elver <elver@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Thierry Reding <treding@...dia.com>,
        mathias.nyman@...ux.intel.com, Qian Cai <cai@....pw>
Subject: Re: BUG: KCSAN: data-race in mutex_spin_on_owner+0xef/0x1b0

On Fri, Dec 04, 2020 at 11:51:39PM +0530, Naresh Kamboju wrote:
> LKFT started testing KCSAN enabled kernel from the linux next tree.
> Here we have found BUG: KCSAN: data-race in mutex_spin_on_owner
> and several more KCSAN BUGs.
> 
> This report is from an x86_64 machine clang-11 linux next 20201201.
> Since we are running for the first time we do not call this regression.
> 
> [    4.745161] usbcore: registered new interface driver cdc_ether
> [    4.751281] ==================================================================
> [    4.756653] usbcore: registered new interface driver net1080
> [    4.752139] BUG: KCSAN: data-race in mutex_spin_on_owner+0xef/0x1b0

At the very least run your splat through ./scripts/decode_stacktrace.sh

It's impossible to know what the thing is complaining about. I suspect
this is one of those known KCSAN 'bugs' where it can't tell a load+cmp0
is perfectly fine.