Re: [PATCH v14 4/5] ring-buffer: Reset RB_MISSED_* flags on persistent ring buffer

[Google]

On Mon, 30 Mar 2026 14:36:13 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Mon, 30 Mar 2026 21:50:20 +0900
> "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> > 
> > Reset RB_MISSED_* flags when the persistent ring buffer is
> > validated at boot. Since these flags are used only in reading
> > process, such process should be stopped when reboot and never
> > be restarted. Thus, these flags are meaningless in the next
> > boot. Moreover, it can confuse the read process after reboot.
> 
> Is it meaningless on a second boot?
> 
> Let's say you have a crash, and there's an invalid buffer. On the next boot
> it is flagged as invalid with the RB_MISSED flag. But then you reboot again
> before looking at the buffer. The next boot will clear this flag. Now
> looking at the persistent ring buffer will not show any missed events.
> 
> Ideally, it shouldn't matter how many reboots are made. If the persistent
> ring buffer hasn't started again, it should always show the same output.

Hmm, OK. I'll drop this.

Thanks!

> 
> -- Steve
> 
> 
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> > ---
> >  Changes in v14:
> >    - Newly added.
> > ---
> >  kernel/trace/ring_buffer.c |    1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> > index e5178239f2f9..5049cf13021e 100644
> > --- a/kernel/trace/ring_buffer.c
> > +++ b/kernel/trace/ring_buffer.c
> > @@ -1903,6 +1903,7 @@ static int rb_validate_buffer(struct buffer_page *bpage, int cpu,
> >  		local_set(&bpage->page->commit, 0);
> >  	} else {
> >  		local_set(&bpage->entries, ret);
> > +		local_set(&bpage->page->commit, tail);
> >  	}
> >  
> >  	return ret;
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>