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

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Message-ID: <alpine.DEB.2.20.1609221555590.5599@nanos>
Date:   Thu, 22 Sep 2016 15:58:03 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jisheng Zhang <jszhang@...vell.com>
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

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?
 
Thanks,

	tglx