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 <[email protected]>
---
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
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 <[email protected]>
> ---
>
> 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;
>
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 <[email protected]>
>> ---
>>
>> 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;
>>
>
> .
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 <[email protected]>
>>> ---
>>>
>>> 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;
>>>
>>
>> .
>
> .
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 <[email protected]>
> ---
> 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.
The following commit has been merged into the perf/core branch of tip:
Commit-ID: 15def34e2635ab7e0e96f1bc32e1b69609f14942
Gitweb: https://git.kernel.org/tip/15def34e2635ab7e0e96f1bc32e1b69609f14942
Author: Yang Jihong <[email protected]>
AuthorDate: Mon, 27 Feb 2023 10:35:08 +08:00
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Fri, 14 Apr 2023 16:08:22 +02:00
perf/core: Fix hardlockup failure caused by perf throttle
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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
---
kernel/events/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index fb3e436..82b95b8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9433,8 +9433,8 @@ __perf_event_account_interrupt(struct perf_event *event, int throttle)
hwc->interrupts = 1;
} else {
hwc->interrupts++;
- if (unlikely(throttle
- && hwc->interrupts >= max_samples_per_tick)) {
+ if (unlikely(throttle &&
+ 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;