linux-kernel - Re: [PATCH] clocksource/drivers/ti-32k: Prevent ftrace recursion

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Date:   Fri, 23 Sep 2016 10:04:31 +0800
From:   Jisheng Zhang <jszhang@...vell.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <daniel.lezcano@...aro.org>, LKML <linux-kernel@...r.kernel.org>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] clocksource/drivers/ti-32k: Prevent ftrace recursion

Hi Thomas,

On Thu, 22 Sep 2016 15:58:03 +0200 Thomas Gleixner wrote:

> On Thu, 22 Sep 2016, Jisheng Zhang wrote:
> 
> > Currently ti-32k can be used as a scheduler clock. We properly marked
> > omap_32k_read_sched_clock() as notrace but we then call another
> > function ti_32k_read_cycles() that _wasn't_ notrace.
> > 
> > Having a traceable function in the sched_clock() path leads to a
> > recursion within ftrace and a kernel crash.  
> 
> Kernel crash? Doesn't ftrace core prevent recursion?

a recent similar issue:

http://www.spinics.net/lists/arm-kernel/msg533480.html

Thanks,
Jisheng