[PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle

[PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle

[Yang Jihong]

commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling")
introduces a change in throttling threshold judgment. Before this,
compare hwc->interrupts and max_samples_per_tick, then increase
hwc->interrupts by 1, but this commit reverses order of these two
behaviors, causing the semantics of max_samples_per_tick to change.
In literal sense of "max_samples_per_tick", if hwc->interrupts ==
max_samples_per_tick, it should not be throttled, therefore, the judgment
condition should be changed to "hwc->interrupts > max_samples_per_tick".

In fact, this may cause the hardlockup to fail, The minimum value of
max_samples_per_tick may be 1, in this case, the return value of
__perf_event_account_interrupt function is 1.
As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
architecture as an example, see x86_pmu_handle_irq).

Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling")
Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
---

Changes since v2:
  - Add fixed commit.

Changes since v1:
  - Modify commit title.

 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index f79fd8b87f75..0540a8653906 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9434,7 +9434,7 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
 	} else {
 		hwc->interrupts++;
 		if (unlikely(throttle
-			     && hwc->interrupts >= max_samples_per_tick)) {
+			     && hwc->interrupts > max_samples_per_tick)) {
 			__this_cpu_inc(perf_throttled_count);
 			tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
 			hwc->interrupts = MAX_INTERRUPTS;
-- 
2.30.GIT

Re: [PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle

[Yang Jihong]

Hello,

PING.

Thanks,
Yang.

On 2023/2/27 10:35, Yang Jihong wrote:
> commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling")
> introduces a change in throttling threshold judgment. Before this,
> compare hwc->interrupts and max_samples_per_tick, then increase
> hwc->interrupts by 1, but this commit reverses order of these two
> behaviors, causing the semantics of max_samples_per_tick to change.
> In literal sense of "max_samples_per_tick", if hwc->interrupts ==
> max_samples_per_tick, it should not be throttled, therefore, the judgment
> condition should be changed to "hwc->interrupts > max_samples_per_tick".
> 
> In fact, this may cause the hardlockup to fail, The minimum value of
> max_samples_per_tick may be 1, in this case, the return value of
> __perf_event_account_interrupt function is 1.
> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
> architecture as an example, see x86_pmu_handle_irq).
> 
> Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling")
> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
> ---
> 
> Changes since v2:
>    - Add fixed commit.
> 
> Changes since v1:
>    - Modify commit title.
> 
>   kernel/events/core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index f79fd8b87f75..0540a8653906 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9434,7 +9434,7 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
>   	} else {
>   		hwc->interrupts++;
>   		if (unlikely(throttle
> -			     && hwc->interrupts >= max_samples_per_tick)) {
> +			     && hwc->interrupts > max_samples_per_tick)) {
>   			__this_cpu_inc(perf_throttled_count);
>   			tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
>   			hwc->interrupts = MAX_INTERRUPTS;
> 

Re: [PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle

[Yang Jihong]

Hello,

PING.

This patch has not been responded.
Please take time to check whether the fix solution is OK.
Look forward to reviewing the patch. Thanks :)

Thanks,
Yang.

On 2023/3/6 9:14, Yang Jihong wrote:
> Hello,
> 
> PING.
> 
> Thanks,
> Yang.
> 
> On 2023/2/27 10:35, Yang Jihong wrote:
>> commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling")
>> introduces a change in throttling threshold judgment. Before this,
>> compare hwc->interrupts and max_samples_per_tick, then increase
>> hwc->interrupts by 1, but this commit reverses order of these two
>> behaviors, causing the semantics of max_samples_per_tick to change.
>> In literal sense of "max_samples_per_tick", if hwc->interrupts ==
>> max_samples_per_tick, it should not be throttled, therefore, the judgment
>> condition should be changed to "hwc->interrupts > max_samples_per_tick".
>>
>> In fact, this may cause the hardlockup to fail, The minimum value of
>> max_samples_per_tick may be 1, in this case, the return value of
>> __perf_event_account_interrupt function is 1.
>> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
>> architecture as an example, see x86_pmu_handle_irq).
>>
>> Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling")
>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>> ---
>>
>> Changes since v2:
>>    - Add fixed commit.
>>
>> Changes since v1:
>>    - Modify commit title.
>>
>>   kernel/events/core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index f79fd8b87f75..0540a8653906 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -9434,7 +9434,7 @@ __perf_event_account_interrupt(struct perf_event 
>> *event, int throttle)
>>       } else {
>>           hwc->interrupts++;
>>           if (unlikely(throttle
>> -                 && hwc->interrupts >= max_samples_per_tick)) {
>> +                 && hwc->interrupts > max_samples_per_tick)) {
>>               __this_cpu_inc(perf_throttled_count);
>>               tick_dep_set_cpu(smp_processor_id(), 
>> TICK_DEP_BIT_PERF_EVENTS);
>>               hwc->interrupts = MAX_INTERRUPTS;
>>
> 
> .

Re: [PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle

[Yang Jihong]

Hello,

PING again.
Look forward the review.

Thanks,
Yang.

On 2023/3/22 15:36, Yang Jihong wrote:
> Hello,
> 
> PING.
> 
> This patch has not been responded.
> Please take time to check whether the fix solution is OK.
> Look forward to reviewing the patch. Thanks :)
> 
> Thanks,
> Yang.
> 
> On 2023/3/6 9:14, Yang Jihong wrote:
>> Hello,
>>
>> PING.
>>
>> Thanks,
>> Yang.
>>
>> On 2023/2/27 10:35, Yang Jihong wrote:
>>> commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling")
>>> introduces a change in throttling threshold judgment. Before this,
>>> compare hwc->interrupts and max_samples_per_tick, then increase
>>> hwc->interrupts by 1, but this commit reverses order of these two
>>> behaviors, causing the semantics of max_samples_per_tick to change.
>>> In literal sense of "max_samples_per_tick", if hwc->interrupts ==
>>> max_samples_per_tick, it should not be throttled, therefore, the 
>>> judgment
>>> condition should be changed to "hwc->interrupts > max_samples_per_tick".
>>>
>>> In fact, this may cause the hardlockup to fail, The minimum value of
>>> max_samples_per_tick may be 1, in this case, the return value of
>>> __perf_event_account_interrupt function is 1.
>>> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
>>> architecture as an example, see x86_pmu_handle_irq).
>>>
>>> Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling")
>>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>>> ---
>>>
>>> Changes since v2:
>>>    - Add fixed commit.
>>>
>>> Changes since v1:
>>>    - Modify commit title.
>>>
>>>   kernel/events/core.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>>> index f79fd8b87f75..0540a8653906 100644
>>> --- a/kernel/events/core.c
>>> +++ b/kernel/events/core.c
>>> @@ -9434,7 +9434,7 @@ __perf_event_account_interrupt(struct 
>>> perf_event *event, int throttle)
>>>       } else {
>>>           hwc->interrupts++;
>>>           if (unlikely(throttle
>>> -                 && hwc->interrupts >= max_samples_per_tick)) {
>>> +                 && hwc->interrupts > max_samples_per_tick)) {
>>>               __this_cpu_inc(perf_throttled_count);
>>>               tick_dep_set_cpu(smp_processor_id(), 
>>> TICK_DEP_BIT_PERF_EVENTS);
>>>               hwc->interrupts = MAX_INTERRUPTS;
>>>
>>
>> .
> 
> .

Re: [PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle

[Peter Zijlstra]

On Mon, Feb 27, 2023 at 10:35:08AM +0800, Yang Jihong wrote:
> commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling")
> introduces a change in throttling threshold judgment. Before this,
> compare hwc->interrupts and max_samples_per_tick, then increase
> hwc->interrupts by 1, but this commit reverses order of these two
> behaviors, causing the semantics of max_samples_per_tick to change.
> In literal sense of "max_samples_per_tick", if hwc->interrupts ==
> max_samples_per_tick, it should not be throttled, therefore, the judgment
> condition should be changed to "hwc->interrupts > max_samples_per_tick".
> 
> In fact, this may cause the hardlockup to fail, The minimum value of
> max_samples_per_tick may be 1, in this case, the return value of
> __perf_event_account_interrupt function is 1.
> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
> architecture as an example, see x86_pmu_handle_irq).
> 
> Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling")
> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
> ---
>  kernel/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index f79fd8b87f75..0540a8653906 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9434,7 +9434,7 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
>  	} else {
>  		hwc->interrupts++;
>  		if (unlikely(throttle
> -			     && hwc->interrupts >= max_samples_per_tick)) {
> +			     && hwc->interrupts > max_samples_per_tick)) {
>  			__this_cpu_inc(perf_throttled_count);
>  			tick_dep_set_cpu(smp_processor_id(), TICK_DEP_BIT_PERF_EVENTS);
>  			hwc->interrupts = MAX_INTERRUPTS;

Thanks, I've made a slight edit to fix the && placement.