From bb9bb45f746b0f9457de9c3fc4da143a6351bdc9 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 10 Jun 2024 14:46:35 +0200 Subject: 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 Reported-by: Xingwei Lee Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20240610124406.359476013@linutronix.de --- arch/x86/events/core.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/x86/events/core.c') diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 5b0dd07b1ef1..acd367c45334 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, -- cgit v1.2.3-58-ga151