linux-kernel - Re: sched: serial port lockdep warning when offlining CPUs

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Message-ID: <20170928110428.ew5ukfihb3bdiszr@sasha-lappy>
Date:   Thu, 28 Sep 2017 11:04:29 +0000
From:   "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Sasha Levin <levinsasha928@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        "pmladek@...e.com" <pmladek@...e.com>,
        "sergey.senozhatsky@...il.com" <sergey.senozhatsky@...il.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>
Subject: Re: sched: serial port lockdep warning when offlining CPUs

On Thu, Sep 28, 2017 at 11:38:47AM +0200, Peter Zijlstra wrote:
>On Thu, Sep 28, 2017 at 02:19:46AM -0700, Sasha Levin wrote:
>> Hi all,
>>
>> I seem to be hitting the following warning when offlining CPUs on the
>> latest -next kernel:
>>
>> [289683102.607076] Unregister pv shared memory for cpu 8
>> [289683102.622922] select_fallback_rq: 3 callbacks suppressed
>
>This is because you hit a printk() from the scheduler, that's known
>broken (along with the rest of printk).
>
>You forgot to actually include that printk() though I suspect it reads
>like:
>
>  "process %d (%s) no longer affine to cpu%d\n"
>
>Now that uses printk_deferred() which _should_ work lots better, but
>clearly the printk() stuff went wobbly again.

Hm, so is this an actual possible lockup, or just a false positive?

>> [289683102.626292] vprintk_emit (kernel/printk/printk.c:1876)
>> [289683102.626294] vprintk_default (kernel/printk/printk.c:1918)
>> [289683102.626295] vprintk_func (kernel/printk/printk_safe.c:382)
>> [289683102.626297] printk (kernel/printk/printk.c:1943)
>> [289683102.626299] ? show_regs_print_info (kernel/printk/printk.c:1943)
>> [289683102.626301] ? lock_acquire (kernel/locking/lockdep.c:4004)
>> [289683102.626306] ___ratelimit (lib/ratelimit.c:52)
>> [289683102.626309] __printk_ratelimit (kernel/printk/printk.c:2874)
>> [289683102.626311] select_fallback_rq (kernel/sched/core.c:1525 (discriminator 1))
>> [289683102.626313] sched_cpu_dying (kernel/sched/core.c:5500 kernel/sched/core.c:5687)
>
>Also, could you pretty please not line wrap logs?

Sure, I had to resort to using gmail at a conference :(

-- 

Thanks,
Sasha