tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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perf: Clean up mediated vPMU accounting

The mediated_pmu_account_event() and perf_create_mediated_pmu()
functions implement the exclusion between '!exclude_guest' counters
and mediated vPMUs. Their implementation is basically identical,
except mirrored in what they count/check.

Make sure the actual implementations reflect this similarity.

Notably:
- while perf_release_mediated_pmu() has an underflow check;
mediated_pmu_unaccount_event() did not.
- while perf_create_mediated_pmu() has an inc_not_zero() path;
mediated_pmu_account_event() did not.

Also, the inc_not_zero() path can be outsite of
perf_mediated_pmu_mutex. The mutex must guard the 0->1 (of either
nr_include_guest_events or nr_mediated_pmu_vms) transition, but once a
counter is already non-zero, it can safely be incremented further.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251208115156.GE3707891@noisy.programming.kicks-ass.net

Peter Zijlstra 3cb3c2f6 3006911f

+7 -2
+7 -2
kernel/events/core.c
··· 6344 6344 if (!is_include_guest_event(event)) 6345 6345 return 0; 6346 6346 6347 - guard(mutex)(&perf_mediated_pmu_mutex); 6347 + if (atomic_inc_not_zero(&nr_include_guest_events)) 6348 + return 0; 6348 6349 6350 + guard(mutex)(&perf_mediated_pmu_mutex); 6349 6351 if (atomic_read(&nr_mediated_pmu_vms)) 6350 6352 return -EOPNOTSUPP; 6351 6353 ··· 6358 6356 static void mediated_pmu_unaccount_event(struct perf_event *event) 6359 6357 { 6360 6358 if (!is_include_guest_event(event)) 6359 + return; 6360 + 6361 + if (WARN_ON_ONCE(!atomic_read(&nr_include_guest_events))) 6361 6362 return; 6362 6363 6363 6364 atomic_dec(&nr_include_guest_events); ··· 6378 6373 */ 6379 6374 int perf_create_mediated_pmu(void) 6380 6375 { 6381 - guard(mutex)(&perf_mediated_pmu_mutex); 6382 6376 if (atomic_inc_not_zero(&nr_mediated_pmu_vms)) 6383 6377 return 0; 6384 6378 6379 + guard(mutex)(&perf_mediated_pmu_mutex); 6385 6380 if (atomic_read(&nr_include_guest_events)) 6386 6381 return -EBUSY; 6387 6382