On Sun, Jun 26, 2022 at 12:53 PM Joe Perches <joe@perches.com> wrote:
>
> In a reply to the printbufs thread, I wrote a proposal to use an
> alloc to reduce stack in vsprintf when CONFIG_KALLSYMS is enabled.
>
> No one has replied to this but I think it's somewhat sensible.

I think that's a bad idea.

Those things are *literally* called from panic situations, which may
be while holding core memory allocation locks, or similar.

The last thing we want to do is make a hard-to-debug panic be even
*harder* to debug because you get a deadlock when oopsing.

(And yes, I realize that the symbol name lookup can have problems too,
but thats' kind of fundamental to %pS, while a kzmalloc isn't.

Now, you are correct that the stack buffer is annoying. But I think
the proper way to fix that is to say "we already *have* the target
buffer, let's use it".

That does require teaching the sprint_symbol() functions that they
need to take a "length of buffer" and return how much they used, but
that would seem to be a sensible thing anyway, and what the code
should always have done?

It's bad policy to just pass in a buffer without length, and I think
it was always broken. Nasty. That KSYM_SYMBOL_LEN is magically taking
care of it all, but it's ugly as heck, wouldn't you say?

NOTE! The attached patch is completely broken.  I did not do that
interface change to the kallsyms code. The patch is literally meant to
be just an explanation of what I mean, not a working patch.

                  Linus