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@gmail.com>
Reported-by: Xingwei Lee <xrivendell7@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20240610124406.359476013@linutronix.de

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 5b0dd07b1ef19e915c1553eb13ca1c20ef1814ff..acd367c45334177e41810522b908c04d3a3dbb56 100644 (file)
--- 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,