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

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Message-ID: <20170928093847.zgcgvxb7ajiaywbr@hirez.programming.kicks-ass.net>
Date:   Thu, 28 Sep 2017 11:38:47 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sasha Levin <levinsasha928@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        alexander.levin@...izon.com, pmladek@...e.com,
        sergey.senozhatsky@...il.com, rostedt@...dmis.org
Subject: Re: sched: serial port lockdep warning when offlining CPUs

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.

> [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?