Re: [PATCH v13 4/4] ring-buffer: Add persistent ring buffer selftest

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Fri, 27 Mar 2026 16:25:08 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Wed, 25 Mar 2026 11:25:25 +0900
> "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > 
> > Add a self-destractive test for the persistent ring buffer. This
> > will invalidate some sub-buffer pages in the persistent ring buffer
> > when kernel gets panic, and check whether the number of detected
> > invalid pages and the total entry_bytes are the same as record
> > after reboot.
> > 
> > This can ensure the kernel correctly recover partially corrupted
> > persistent ring buffer when boot.
> > 
> > The test only runs on the persistent ring buffer whose name is
> > "ptracingtest". And user has to fill it up with events before
> > kernel panics.
> > 
> > To run the test, enable CONFIG_RING_BUFFER_PERSISTENT_SELFTEST
> 
> I think a more appropriate config name would be:
> 
>   CONFIG_PERSISTENT_RING_BUFFER_ERROR_INJECT
> 
> as that's what it is doing as it is only testing error injection and not
> the persistent ring buffer.

OK, selftest will be another implementation.

(preparing buffer with test data and check recovery process?)

> 
> > and you have to setup the kernel cmdline;
> > 
> >  reserve_mem=20M:2M:trace trace_instance=ptracingtest^traceoff@trace
> >  panic=1
> > 
> > And run following commands after the 1st boot;
> > 
> >  cd /sys/kernel/tracing/instances/ptracingtest
> >  echo 1 > tracing_on
> >  echo 1 > events/enable
> >  sleep 3
> >  echo c > /proc/sysrq-trigger
> 
> These instructions should probably be in the CONFIG help message.

OK. I'll add it.

> 
> > 
> > After panic message, the kernel will reboot and run the verification
> > on the persistent ring buffer, e.g.
> > 
> >  Ring buffer meta [2] invalid buffer page detected
> >  Ring buffer meta [2] is from previous boot! (318 pages discarded)
> >  Ring buffer testing [2] invalid pages: PASSED (318/318)
> >  Ring buffer testing [2] entry_bytes: PASSED (1300476/1300476)
> 
> BTW, when I tested this, I got the above on the first boot, but if I
> rebooted normally without re-enabling the persistent ring buffer, I would
> get on the next boot:

Hmm, since it is already recovered (rewound) the 2nd rewound process
may not work correctly. Let me fix it.
> 
> 
> [    0.966510] Ring buffer meta [2] is from previous boot! (0 pages discarded)
> [    0.971338]  #2
> [    1.003431] Ring buffer meta [3] is from previous boot! (0 pages discarded)
> [    1.007737]  #3
> [    1.039091] Ring buffer meta [4] is from previous boot! (0 pages discarded)
> [    1.043181] Ring buffer testing [4] invalid pages: FAILED (0/1597)
> [    1.044660] Ring buffer testing [4] entry_bytes: PASSED (6512464/6512464)
> [    1.047829]  #4
> [    1.079811] Ring buffer meta [5] is from previous boot! (0 pages discarded)
> [    1.083728]  #5
> [    1.116764] Ring buffer meta [6] is from previous boot! (0 pages discarded)
> [    1.120846]  #6
> [    1.156502] Ring buffer meta [7] is from previous boot! (0 pages discarded)
> [    1.160857]  #7
> 
> I'll start testing the previous 3 patches and may add them to next.

Thanks,

> 
> Also, I noticed that there's nothing that reads the RB_MISSING as I thought
> it might. I'll have to look into how to pass that info to the trace output.
> 
> -- Steve
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>