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SubjectRe: [PATCH 3/3] lockdep: Use line-buffered printk() for lockdep messages.
On (11/08/18 12:53), Petr Mladek wrote:
> > lockdep.c
> > printk_safe_enter_irqsave(flags);
> > lockdep_report();
> > printk_safe_exit_irqrestore(flags);
> All this looks nice. Let's look it also from the other side.
> The following comes to my mind:
> a) lockdep is not the only place when continuous lines get mixed.
> This patch mentions also RCU stalls. The other patch mentions
> OOM. I am sure that there will be more.
> b) It is not obvious where printk_safe() would be necessary.
> While buffered printk is clearly connected with continuous
> lines.
> c) I am not sure that disabling preemption would always be
> acceptable.
> d) We might need to increase the size of the per-CPU buffers if
> they are used more widely.
> e) People would need to learn a new (printk_safe) API when it is
> use outside printk sources.
> f) Losing the entire log is more painful than loosing one line
> when the buffer never gets flushed.
> Sigh, no solution is perfect. If only we could agree that one
> way was better than the other.

I agree with what you are saying. All of the above (in my email)
was for lockdep only, that's why I did mention lockdep several times.
Like I said, a random and wild idea.
I'm not proposing printk_safe as a "better" buffered printk for
everyone. The buffered_printk patch is pretty big, and comes with a
price tag.

If lockdep and OOM people will ACK buffered printk transition in
its current form, then we can go ahead.

It's debatable if we need a fixed size list of buffers; or we can
do kmalloc()+cont fallback. But if we will have ACKs, then we can
move forward.


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