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

[Steven Rostedt]

On Wed, 25 Mar 2026 11:25:25 +0900
"Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> 
> 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.

> 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.

> 
> 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:


[    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.

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