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

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commit a91f86e270 upstream.

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
is part 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;
  }

Cc: stable@vger.kernel.org
Fixes: b37042b2bb ("LoongArch: Add perf events support")
Signed-off-by: Lisa Robinson <lisa@bytefly.space>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

This commit is contained in:

Lisa Robinson 2026-01-17 10:56:43 +08:00 • committed by Greg Kroah-Hartman

parent 78b4eb9975

commit 5b14ce4975

1 changed files with 18 additions and 3 deletions

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arch/loongarch/kernel/perf_event.c

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