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SubjectRe: [PATCH 19/19] [INCOMPLETE] ARM: make return_address available for ARM_UNWIND
On Fri, Jan 25, 2013 at 11:44:14AM -0500, Steven Rostedt wrote:
> [ I got an error with linux-arm-kernel@list.infradead.org and had to
> remove from CC ]

Blame Arnd :)

>
> On Fri, 2013-01-25 at 16:26 +0000, Dave Martin wrote:
>
> > However, if the purpose if making return_address() notrace is just to
> > prevent infinite recursion, where finite recursion is safe, then it
> > feels fixable as described above.
> >
> > Steven, do you know whether such an approach might be safe?
> >
>
> I rewrote the function trace recursion code (see linux-next). The
> function tracer wont recurse on itself. If the return_address() is only
> used by callbacks and not directly by the mcount(ftrace_caller), then
> after the first trace, ftrace wont let recursion of the callback. IOW,
> callbacks of ftrace don't need to worry about re-entrancy at the same
> context level (but do for different contexts, ie. normal, irq, softirq
> and NMI).
>
> (commit edc15cafcbfa3d73f819cae99885a2e35e4cbce5 in linux-next and
> friends)

Cool. Are you aware of return_address being used elsewhere? Currently
I'm not aware of anything else which uses it, and grep is not finding
any calls outside ftrace.h that I can see.

Cheers
---Dave


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