From 3376c19b81e0e4643eb18342f9ce7b652815d20c Mon Sep 17 00:00:00 2001 From: Ding Tianhong Date: Wed, 30 Aug 2017 19:41:00 +0200 Subject: [PATCH] clocksource/drivers/arm_arch_timer: Avoid infinite recursion when ftrace is enabled BugLink: https://bugs.launchpad.net/bugs/1713821 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 Acked-by: Mark Rutland Acked-by: Marc Zyngier Signed-off-by: Daniel Lezcano (cherry picked from commit adb4f11e0a8f4e29900adb2b7af28b6bbd5c1fa4) Signed-off-by: dann frazier Acked-by: Stefan Bader Acked-by: Colin King Signed-off-by: Stefan Bader --- 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 a79c6932bf3f..7c6c24fafb90 100644 --- a/arch/arm64/include/asm/arch_timer.h +++ b/arch/arm64/include/asm/arch_timer.h @@ -66,13 +66,13 @@ 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); \ } \ -- 2.39.2