linux-kernel - Re: [tracing] 06e0a548ba: WARNING:at_kernel/trace/ring_buffer.c:#ring_buffer_iter

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Message-ID: <20200513122524.2352c105@gandalf.local.home>
Date:   Wed, 13 May 2020 12:25:24 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sven Schnelle <svens@...ux.ibm.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org
Subject: Re: [tracing] 06e0a548ba:
 WARNING:at_kernel/trace/ring_buffer.c:#ring_buffer_iter_peek

On Wed, 13 May 2020 18:15:57 +0200
Sven Schnelle <svens@...ux.ibm.com> wrote:

> Thanks for looking into this. I've attached my /proc/config.gz to this Mail.
> The x86 system is my Laptop which is a Thinkpad X280 with 4 HT CPUs (so 8 cpus
> in total). I've tried disabling preemption, but this didn't help.
> 
> It's always this check that causes the loop:
> 
> if (iter->head >= rb_page_size(iter->head_page)) {
> 	rb_inc_iter(iter);
> 	goto again;
> }
> 
> On the first loop iter->head is some value > 0 and rb_page_size returns
> 0, afterwards it gets twice to this check with both values 0. The third
> time the warning is triggered. Maybe that information helps.

Letting it run long enough, I was able to trigger it.

I think I know what's wrong with it. I'll put in some debugging to see if
my thoughts are accurate.

Thanks for bringing this back to my attention.

-- Steve