linux-kernel - [tip: locking/core] perf/x86: Serialize set_attr

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Date: Mon, 17 Jun 2024 15:47:19 -0000
From: "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Yue Sun <samsun1006219@...il.com>, Xingwei Lee <xrivendell7@...il.com>,
 Thomas Gleixner <tglx@...utronix.de>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: locking/core] perf/x86: Serialize set_attr_rdpmc()

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     bb9bb45f746b0f9457de9c3fc4da143a6351bdc9
Gitweb:        https://git.kernel.org/tip/bb9bb45f746b0f9457de9c3fc4da143a6351bdc9
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Mon, 10 Jun 2024 14:46:35 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 11 Jun 2024 11:25:22 +02:00

perf/x86: Serialize set_attr_rdpmc()

Yue and Xingwei reported a jump label failure. It's caused by the lack of
serialization in set_attr_rdpmc():

CPU0                           CPU1

Assume: x86_pmu.attr_rdpmc == 0

if (val != x86_pmu.attr_rdpmc) {
  if (val == 0)
    ...
  else if (x86_pmu.attr_rdpmc == 0)
    static_branch_dec(&rdpmc_never_available_key);

				if (val != x86_pmu.attr_rdpmc) {
				   if (val == 0)
				      ...
				   else if (x86_pmu.attr_rdpmc == 0)
     FAIL, due to imbalance --->      static_branch_dec(&rdpmc_never_available_key);

The reported BUG() is a consequence of the above and of another bug in the
jump label core code. The core code needs a separate fix, but that cannot
prevent the imbalance problem caused by set_attr_rdpmc().

Prevent this by serializing set_attr_rdpmc() locally.

Fixes: a66734297f78 ("perf/x86: Add /sys/devices/cpu/rdpmc=2 to allow rdpmc for all tasks")
Closes: https://lore.kernel.org/r/CAEkJfYNzfW1vG=ZTMdz_Weoo=RXY1NDunbxnDaLyj8R4kEoE_w@mail.gmail.com
Reported-by: Yue Sun <samsun1006219@...il.com>
Reported-by: Xingwei Lee <xrivendell7@...il.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20240610124406.359476013@linutronix.de
---
 arch/x86/events/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 5b0dd07..acd367c 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2547,6 +2547,7 @@ static ssize_t set_attr_rdpmc(struct device *cdev,
 			      struct device_attribute *attr,
 			      const char *buf, size_t count)
 {
+	static DEFINE_MUTEX(rdpmc_mutex);
 	unsigned long val;
 	ssize_t ret;
 
@@ -2560,6 +2561,8 @@ static ssize_t set_attr_rdpmc(struct device *cdev,
 	if (x86_pmu.attr_rdpmc_broken)
 		return -ENOTSUPP;
 
+	guard(mutex)(&rdpmc_mutex);
+
 	if (val != x86_pmu.attr_rdpmc) {
 		/*
 		 * Changing into or out of never available or always available,