1. Patchew
  2. linux
  3. View series

[PATCH] LoongArch: Fix PMU counter allocation for mixed-type event groups

Lisa Robinson posted 1 patch 1 month, 1 week ago
There is a newer version of this series
arch/loongarch/kernel/perf_event.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
[PATCH] LoongArch: Fix PMU counter allocation for mixed-type event groups
Posted by Lisa Robinson 1 month, 1 week ago 
When validating a perf event group, validate_group() unconditionally
attempts to allocate hardware PMU counters for the leader, sibling
events and the new event being added.

This is incorrect for mixed-type groups. If a PERF_TYPE_SOFTWARE event
ispart of the group, the current code still tries to allocate a hardware
PMU counter for it, which can wrongly consume hardware PMU resources and
cause spurious allocation failures.

Fix this by only allocating PMU counters for hardware events during group
validation, and skipping software events.

A trimmed down reproducer is as simple as this:

  #include <stdio.h>
  #include <assert.h>
  #include <unistd.h>
  #include <string.h>
  #include <sys/syscall.h>
  #include <linux/perf_event.h>

  int
  main (int argc, char *argv[])
  {
  	struct perf_event_attr attr = { 0 };
  	int fds[5];

  	attr.disabled = 1;
  	attr.exclude_kernel = 1;
  	attr.exclude_hv = 1;
  	attr.read_format = PERF_FORMAT_TOTAL_TIME_ENABLED |
  		PERF_FORMAT_TOTAL_TIME_RUNNING | PERF_FORMAT_ID | PERF_FORMAT_GROUP;
  	attr.size = sizeof (attr);

  	attr.type = PERF_TYPE_SOFTWARE;
  	attr.config = PERF_COUNT_SW_DUMMY;
  	fds[0] = syscall (SYS_perf_event_open, &attr, 0, -1, -1, 0);
  	assert (fds[0] >= 0);

  	attr.type = PERF_TYPE_HARDWARE;
  	attr.config = PERF_COUNT_HW_CPU_CYCLES;
  	fds[1] = syscall (SYS_perf_event_open, &attr, 0, -1, fds[0], 0);
  	assert (fds[1] >= 0);

  	attr.type = PERF_TYPE_HARDWARE;
  	attr.config = PERF_COUNT_HW_INSTRUCTIONS;
  	fds[2] = syscall (SYS_perf_event_open, &attr, 0, -1, fds[0], 0);
  	assert (fds[2] >= 0);

  	attr.type = PERF_TYPE_HARDWARE;
  	attr.config = PERF_COUNT_HW_BRANCH_MISSES;
  	fds[3] = syscall (SYS_perf_event_open, &attr, 0, -1, fds[0], 0);
  	assert (fds[3] >= 0);

  	attr.type = PERF_TYPE_HARDWARE;
  	attr.config = PERF_COUNT_HW_CACHE_REFERENCES;
  	fds[4] = syscall (SYS_perf_event_open, &attr, 0, -1, fds[0], 0);
  	assert (fds[4] >= 0);

  	printf ("PASSED\n");

  	return 0;
  }

Fixes: b37042b2bb7c ("LoongArch: Add perf events support")
Signed-off-by: Lisa Robinson <lisa@bytefly.space>
---
 arch/loongarch/kernel/perf_event.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/loongarch/kernel/perf_event.c b/arch/loongarch/kernel/perf_event.c
index 9d257c8519c9..82cc08c2b056 100644
--- a/arch/loongarch/kernel/perf_event.c
+++ b/arch/loongarch/kernel/perf_event.c
@@ -633,15 +633,24 @@ static int validate_group(struct perf_event *event)
 
 	memset(&fake_cpuc, 0, sizeof(fake_cpuc));
 
-	if (loongarch_pmu_alloc_counter(&fake_cpuc, &leader->hw) < 0)
+	if ((PERF_TYPE_HARDWARE == leader->attr.type ||
+	     PERF_TYPE_HW_CACHE == leader->attr.type ||
+	     PERF_TYPE_RAW == leader->attr.type) &&
+	    loongarch_pmu_alloc_counter(&fake_cpuc, &leader->hw) < 0)
 		return -EINVAL;
 
 	for_each_sibling_event(sibling, leader) {
-		if (loongarch_pmu_alloc_counter(&fake_cpuc, &sibling->hw) < 0)
+		if ((PERF_TYPE_HARDWARE == sibling->attr.type ||
+		     PERF_TYPE_HW_CACHE == sibling->attr.type ||
+		     PERF_TYPE_RAW == sibling->attr.type) &&
+		    loongarch_pmu_alloc_counter(&fake_cpuc, &sibling->hw) < 0)
 			return -EINVAL;
 	}
 
-	if (loongarch_pmu_alloc_counter(&fake_cpuc, &event->hw) < 0)
+	if ((PERF_TYPE_HARDWARE == event->attr.type ||
+	     PERF_TYPE_HW_CACHE == event->attr.type ||
+	     PERF_TYPE_RAW == event->attr.type) &&
+	    loongarch_pmu_alloc_counter(&fake_cpuc, &event->hw) < 0)
 		return -EINVAL;
 
 	return 0;
-- 
2.52.0
Re: [PATCH] LoongArch: Fix PMU counter allocation for mixed-type event groups
Posted by Mi, Dapeng 1 month ago 
On 12/31/2025 5:15 PM, Lisa Robinson wrote:
> When validating a perf event group, validate_group() unconditionally
> attempts to allocate hardware PMU counters for the leader, sibling
> events and the new event being added.
>
> This is incorrect for mixed-type groups. If a PERF_TYPE_SOFTWARE event
> ispart of the group, the current code still tries to allocate a hardware
> PMU counter for it, which can wrongly consume hardware PMU resources and
> cause spurious allocation failures.
>
> Fix this by only allocating PMU counters for hardware events during group
> validation, and skipping software events.
>
> A trimmed down reproducer is as simple as this:
>
>   #include <stdio.h>
>   #include <assert.h>
>   #include <unistd.h>
>   #include <string.h>
>   #include <sys/syscall.h>
>   #include <linux/perf_event.h>
>
>   int
>   main (int argc, char *argv[])
>   {
>   	struct perf_event_attr attr = { 0 };
>   	int fds[5];
>
>   	attr.disabled = 1;
>   	attr.exclude_kernel = 1;
>   	attr.exclude_hv = 1;
>   	attr.read_format = PERF_FORMAT_TOTAL_TIME_ENABLED |
>   		PERF_FORMAT_TOTAL_TIME_RUNNING | PERF_FORMAT_ID | PERF_FORMAT_GROUP;
>   	attr.size = sizeof (attr);
>
>   	attr.type = PERF_TYPE_SOFTWARE;
>   	attr.config = PERF_COUNT_SW_DUMMY;
>   	fds[0] = syscall (SYS_perf_event_open, &attr, 0, -1, -1, 0);
>   	assert (fds[0] >= 0);
>
>   	attr.type = PERF_TYPE_HARDWARE;
>   	attr.config = PERF_COUNT_HW_CPU_CYCLES;
>   	fds[1] = syscall (SYS_perf_event_open, &attr, 0, -1, fds[0], 0);
>   	assert (fds[1] >= 0);
>
>   	attr.type = PERF_TYPE_HARDWARE;
>   	attr.config = PERF_COUNT_HW_INSTRUCTIONS;
>   	fds[2] = syscall (SYS_perf_event_open, &attr, 0, -1, fds[0], 0);
>   	assert (fds[2] >= 0);
>
>   	attr.type = PERF_TYPE_HARDWARE;
>   	attr.config = PERF_COUNT_HW_BRANCH_MISSES;
>   	fds[3] = syscall (SYS_perf_event_open, &attr, 0, -1, fds[0], 0);
>   	assert (fds[3] >= 0);
>
>   	attr.type = PERF_TYPE_HARDWARE;
>   	attr.config = PERF_COUNT_HW_CACHE_REFERENCES;
>   	fds[4] = syscall (SYS_perf_event_open, &attr, 0, -1, fds[0], 0);
>   	assert (fds[4] >= 0);
>
>   	printf ("PASSED\n");
>
>   	return 0;
>   }
>
> Fixes: b37042b2bb7c ("LoongArch: Add perf events support")
> Signed-off-by: Lisa Robinson <lisa@bytefly.space>
> ---
>  arch/loongarch/kernel/perf_event.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/arch/loongarch/kernel/perf_event.c b/arch/loongarch/kernel/perf_event.c
> index 9d257c8519c9..82cc08c2b056 100644
> --- a/arch/loongarch/kernel/perf_event.c
> +++ b/arch/loongarch/kernel/perf_event.c
> @@ -633,15 +633,24 @@ static int validate_group(struct perf_event *event)
>  
>  	memset(&fake_cpuc, 0, sizeof(fake_cpuc));
>  
> -	if (loongarch_pmu_alloc_counter(&fake_cpuc, &leader->hw) < 0)
> +	if ((PERF_TYPE_HARDWARE == leader->attr.type ||
> +	     PERF_TYPE_HW_CACHE == leader->attr.type ||
> +	     PERF_TYPE_RAW == leader->attr.type) &&

Better introduce an inline function to check these event types instead of
duplicating same code.


> +	    loongarch_pmu_alloc_counter(&fake_cpuc, &leader->hw) < 0)
>  		return -EINVAL;
>  
>  	for_each_sibling_event(sibling, leader) {
> -		if (loongarch_pmu_alloc_counter(&fake_cpuc, &sibling->hw) < 0)
> +		if ((PERF_TYPE_HARDWARE == sibling->attr.type ||
> +		     PERF_TYPE_HW_CACHE == sibling->attr.type ||
> +		     PERF_TYPE_RAW == sibling->attr.type) &&
> +		    loongarch_pmu_alloc_counter(&fake_cpuc, &sibling->hw) < 0)
>  			return -EINVAL;
>  	}
>  
> -	if (loongarch_pmu_alloc_counter(&fake_cpuc, &event->hw) < 0)
> +	if ((PERF_TYPE_HARDWARE == event->attr.type ||
> +	     PERF_TYPE_HW_CACHE == event->attr.type ||
> +	     PERF_TYPE_RAW == event->attr.type) &&
> +	    loongarch_pmu_alloc_counter(&fake_cpuc, &event->hw) < 0)
>  		return -EINVAL;
>  
>  	return 0;

Patchew 2.1-devel-b67e4c2

© 2016 - 2026 Red Hat, Inc.