Messages in this thread | | | Subject | Re: [PATCH RESEND] arm64: arch_timer: fix the infinite recursion when enable ftrace and erratum workaround | From | Marc Zyngier <> | Date | Mon, 10 Jul 2017 14:54:27 +0100 |
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On 10/07/17 12:22, Mark Rutland wrote: > On Sun, Jul 09, 2017 at 04:30:54PM +0800, Ding Tianhong wrote: >> When enable preempt and debug ftrace, and perform the following steps, the >> system will hang: >> mount -t debugfs nodev /sys/kernel/debug/ >> cd /sys/kernel/debug/tracing/ >> echo function_graph > current_tracer >> >> This is because tracing the preempt_disable/enable calls would cause >> trace_clock() which would get local timer to go into infinite recursion >> when enable the arch timer erratum workaround for some chips, so Prevent >> tracing of preempt_disable/enable() in arch_timer_reg_read_stable(). >> >> This problem is similar to the fixed by upstream commit 96b3d28bf4 >> ("sched/clock: Prevent tracing recursion in sched_clock_cpu()"). > > As I mentioned before, the patch itself looks fine to me, but the commit > message is somewhat difficult to read. > > Can we please change this to: > > arm64: arch_timer: avoid infinite recursion when ftrace is enabled > > On platforms with an arch timer erratum workaround, it's possible for > arch_timer_reg_read_stable() to recurse into itself when certain > tracing options are enabled, leading to stack overflows and related > problems. > > For example, when PREEMPT_TRACER and FUNCTION_GRAPH_TRACER are > selected, it's possible to trigger this with: > > $ mount -t debugfs nodev /sys/kernel/debug/ > $ echo function_graph > /sys/kernel/debug/tracing/current_tracer > > The problem is that in such cases, preempt_disable() instrumentation > attempts to acquire a timestamp via trace_clock(), resulting in a call > back to arch_timer_reg_read_stable(), and hence recursion. > > This patch changes arch_timer_reg_read_stable() to use > preempt_{disable,enable}_notrace(), which avoids this. > > With that commit message: > > Acked-by: Mark Rutland <mark.rutland@arm.com> > > Daniel, Thomas, would you be happy to fold that in when picking this? Or > would you prefer that I fix this up and resend?
With the proposed changes:
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
M. -- Jazz is not dead. It just smells funny...
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