linux-kernel - Re: [BUG] NULL pointer dereference probably caused by kernel/trace/ring

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Date:   Tue, 1 Nov 2022 17:38:02 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Roland Ruckerbauer <roland.rucky@...il.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org, Takashi Iwai <tiwai@...e.de>,
        regressions@...ts.linux.dev,
        Steven Noonan <steven.noonan@...il.com>
Subject: Re: [BUG] NULL pointer dereference probably caused by
 kernel/trace/ring_buffer.c

On Tue, 1 Nov 2022 21:07:20 +0100
Roland Ruckerbauer <roland.rucky@...il.com> wrote:

> Meaning the rbwork pointer is not null, but also not a valid pointer.
> Subtracting offset of the wait_index gives me address 0x178, which
> sure seems wrong.

Hmm, I wonder if the buffer got freed somehow. Not sure how that would
happen, as you can't free the buffer if something is opened on it.

> 
> I think I will try a gdb session with this kernel (but I have not done
> this for a long time, might take me a while to get it working).

If this is fully reproducible, could you run strace -f on rasdaemon to
see what it is doing before it crashed?

That could be very useful. At least I may be able to create a
reproducer, as my rasdaemon is working fine.

-- Steve