linux-kernel - Re: [PATCH 19/19] [INCOMPLETE] ARM: make return_address available for ARM

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Message-ID: <1359132254.21576.230.camel@gandalf.local.home>
Date:	Fri, 25 Jan 2013 11:44:14 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Dave Martin <dave.martin@...aro.org>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	sahara <keun-o.park@...driver.com>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH 19/19] [INCOMPLETE] ARM: make return_address available
 for ARM_UNWIND

[ I got an error with linux-arm-kernel@...t.infradead.org and had to
remove from CC ]

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)

-- Steve


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