[v2] arm64: arch_timer: avoid infinite recursion when ftrace is enabled

Message ID a53349bd-aa6c-cdc1-1476-a068a5cfc2c2@huawei.com
State New
Headers show

Commit Message

Ding Tianhong Aug. 10, 2017, 2:52 a.m.
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>

---
 arch/arm64/include/asm/arch_timer.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

-- 
1.9.0

Comments

Ding Tianhong Aug. 10, 2017, 3:33 a.m. | #1
add Danial and Thomas.

On 2017/8/10 10:52, Ding Tianhong wrote:
> 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>

> ---

>  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);				\

>  	}								\

>

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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);				\
 	}								\