[tip: perf/urgent] perf/core: Fix low freq setting via IOC_PERIOD

[tip-bot2 for Kan Liang]

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     0d39844150546fa1415127c5fbae26db64070dd3
Gitweb:        https://git.kernel.org/tip/0d39844150546fa1415127c5fbae26db64070dd3
Author:        Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
AuthorDate:    Fri, 17 Jan 2025 07:19:12 -08:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 25 Feb 2025 14:54:14 +01:00

perf/core: Fix low freq setting via IOC_PERIOD

A low attr::freq value cannot be set via IOC_PERIOD on some platforms.

The perf_event_check_period() introduced in:

  81ec3f3c4c4d ("perf/x86: Add check_period PMU callback")

was intended to check the period, rather than the frequency.
A low frequency may be mistakenly rejected by limit_period().

Fix it.

Fixes: 81ec3f3c4c4d ("perf/x86: Add check_period PMU callback")
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20250117151913.3043942-2-kan.liang@xxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/lkml/20250115154949.3147-1-ravi.bangoria@xxxxxxx/
---
 kernel/events/core.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 086d46d..6364319 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5969,14 +5969,15 @@ static int _perf_event_period(struct perf_event *event, u64 value)
 	if (!value)
 		return -EINVAL;
 
-	if (event->attr.freq && value > sysctl_perf_event_sample_rate)
-		return -EINVAL;
-
-	if (perf_event_check_period(event, value))
-		return -EINVAL;
-
-	if (!event->attr.freq && (value & (1ULL << 63)))
-		return -EINVAL;
+	if (event->attr.freq) {
+		if (value > sysctl_perf_event_sample_rate)
+			return -EINVAL;
+	} else {
+		if (perf_event_check_period(event, value))
+			return -EINVAL;
+		if (value & (1ULL << 63))
+			return -EINVAL;
+	}
 
 	event_function_call(event, __perf_event_period, &value);