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

[Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>]

 > | 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.
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