Messages in this thread Patch in this message | | | From | Daniel Lezcano <> | Subject | [PATCH 5/5] clocksource/drivers/arm_arch_timer: Avoid infinite recursion when ftrace is enabled | Date | Fri, 11 Aug 2017 16:17:41 +0200 |
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From: Ding Tianhong <dingtianhong@huawei.com>
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.
This problem is similar to the fixed by upstream commit 96b3d28bf4 ("sched/clock: Prevent tracing recursion in sched_clock_cpu()").
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> Acked-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Marc Zyngier <marc.zyngier@arm.com> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org> --- 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..a652ce0 100644 --- a/arch/arm64/include/asm/arch_timer.h +++ b/arch/arm64/include/asm/arch_timer.h @@ -65,13 +65,13 @@ DECLARE_PER_CPU(const 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); \ } \ -- 2.7.4
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