Re: [PATCH v2] arm64: arch_timer: avoid infinite recursion when ftrace is enabled
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
> Acked-by: Mark Rutland
> Acked-by: Marc Zyngier
> ---
> 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);\
> } \
>
Re: [PATCH v2] arm64: arch_timer: avoid infinite recursion when ftrace is enabled
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
> Acked-by: Mark Rutland
> Acked-by: Marc Zyngier
> ---
> 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);\
> } \
>
[PATCH v2] 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.
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
---
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
[PATCH v2] 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.
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
---
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
