linux-kernel - Re: [PATCH v3] pstore/ftrace: Convert to its own enable/disable debugfs knob

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Date:	Tue, 21 Aug 2012 19:10:17 -0700
From:	Anton Vorontsov <cbouatmailru@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Shuah Khan <shuahkhan@...il.com>, arve@...roid.com,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	Jesper Juhl <jj@...osbits.net>,
	Randy Dunlap <rdunlap@...otime.net>,
	Thomas Meyer <thomas@...3r.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com, Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH v3] pstore/ftrace: Convert to its own enable/disable
 debugfs knob

On Tue, Aug 21, 2012 at 09:07:19PM -0400, Steven Rostedt wrote: [...]
> I'm fine with it. I know there was some issues about recursion
> protection and I said that the function tracer now has its own
> protection where you don't need to worry about it. I was hoping that
> code would make it into 3.6, but Linus opened the merge window the day
> after I posted the final version. Which I figured was too close to the
> merge window to push for 3.6 (lots of changes occurred, and I wanted
> it vetted in linux-next for a bit).
> 
> Now those changes are queued for 3.7 and are currently in the tip
> tree.  You can supply your own temporary recursion protection to the
> function tracer callback, or wait till my changes make it into Linus's
> tree.

Great! Btw, the particular recursion issue that I faced back then was
triggered by a missing 'notrace' specifier for the ->write() callback in
pstore code, i.e. a bug in pstore.

Running without any recursion protection is prone to weird
lockups/reboots, and probably a good idea to have it on a production
system. But recursion during tracing is still an evidence of some other
bugs, right? At least the fact that I didn't have it helped me to find a
bug. So, does it make sense to make the recursion protection optionally
disabled? Maybe as some CONFIG_DEBUG_* option (briefly looking into
kernel/trace/Kconfig I didn't find any)?

Thanks,

Anton.
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