clocksource/drivers/arm_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.

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>

diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
index 74d08e44a651b9e58de7d8a6075f6101083f5262..a652ce0a5cb2c33178ac2e447fad1159efb0c6a9 100644 (file)
--- 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);                                \
        }                                                               \