On (21/03/22 11:53), John Ogness wrote:
> On 2021-03-21, Sergey Senozhatsky <senozhat...@chromium.org> wrote:
> >> @@ -2055,6 +2122,9 @@ int vprintk_store(int facility, int level,
> >> */
> >> ts_nsec = local_clock();
> >>
> >> + if (!printk_enter_irqsave(&irqflags))
> >> + return 0;
> >
> > I guess it can be interesting to somehow signal us that we had
> > printk() recursion overflow, and how many messages we lost.
>
> Honestly, if we hit 3 levels of recursion, we are probably dealing with
> an infinite recursion issue.
I tend to agree.
> I do not see the value of counting the overflows in that case. The
> logged messages at that recursion level would ben enough to point
> us to the problem.
>
> > 3 levels of recursion seem like reasonable limit, but I maybe wouldn't
> > mind one extra level.
>
> With 3 levels, we will see all the messages of:
>
> printk -> WARN_ON -> WARN_ON -> WARN_ON
Well, not necessarily this simple.
printk
vsprintf
handle_foo_specifier
printk
call_console_drivers
timekeeping
printk
vsprintf
We saw in the past that enabling CONFIG_DEBUG_OBJECTS (if I'm not
mistaken) can add quite a bit of extra printk recursion paths.
We also have other CONFIG_DEBUG_* config options that can pop up as
recursive printk-s here and there. For instance, from vsprintf::foo_specifier()
where we escape from printk() to various kernel subsystems: net, block,
etc.
Maybe sometimes on level 3+ we'll see something interesting,
but I've no strong opinion on this.
> Keep in mind that each additional level causes the reading of the logs
> to be significantly more complex. Each level increases the output
> exponentially:
Yes, I realize that. That's why I suggested that maybe recursive
printk-s can have some special extra prefix. Recursive printk-s
will interleave with whatever is being printed on this_cpu, so
prefix might be helpful.
-ss
