Re: [PATCH 39/53] IB/qib: Add qib_trace.c

Roland Dreier
2009-11-24T04:09:35Z

> | I don't think random PCI device drivers hooking into the panic notifier
> | chain is really a good idea, so probably ripping this out for now is the
> | best thing to do.
>
> It's extremely useful to have this, otherwise no trace info gets out
> when the system panics (one of the big reasons you want tracing
> in the first place).
>
> As best as I can tell, the panic hooks are intended for just this kind
> of thing. If there's some other mechanism, we'd be happy to use it.

I can't find one other "non-special" driver hooking into the panic
notifier. (The only uses appear to be console drivers doing flushing to
make sure that panic messages actually appear) Which should be a hint
that you probably don't really need it either.

Really, all this duplicated tracing infrastructure is a no-go. Take a
look at ftrace events; they're pretty much awesome. Look in
Documentation/trace and for a practical example all the trace_ext4_xxx
stuff in fs/ext4. Then you can add a generic mechanism to dump the
trace buffer on panic; I think the tracing guys would be supportive of
that, it makes a lot of sense for debugging.

- R.