Messages in this thread | | | Subject | Re: [PATCH RESEND] arm64: arch_timer: fix the infinite recursion when enable ftrace and erratum workaround | From | Ding Tianhong <> | Date | Wed, 26 Jul 2017 10:42:49 +0800 |
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On 2017/7/10 19:22, 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? >
Hi Danial, Thomas:
It looks didn't merge to the mainline tree yet, should I update the commit and resend this patch again?
Thanks Ding
> Thanks, > Mark. > >> Fixes: 6acc71ccac71 ("arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs") >> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com> >> --- >> arch/arm64/include/asm/arch_timer.h | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h >> index 74d08e4..67bb7a4 100644 >> --- a/arch/arm64/include/asm/arch_timer.h >> +++ b/arch/arm64/include/asm/arch_timer.h >> @@ -65,13 +65,13 @@ struct arch_timer_erratum_workaround { >> u64 _val; \ >> if (needs_unstable_timer_counter_workaround()) { \ >> const struct arch_timer_erratum_workaround *wa; \ >> - preempt_disable(); \ >> + preempt_disable_notrace(); \ >> wa = __this_cpu_read(timer_unstable_counter_workaround); \ >> if (wa && wa->read_##reg) \ >> _val = wa->read_##reg(); \ >> else \ >> _val = read_sysreg(reg); \ >> - preempt_enable(); \ >> + preempt_enable_notrace(); \ >> } else { \ >> _val = read_sysreg(reg); \ >> } \ >> -- >> 1.9.0 >> >> > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > . >
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