Commit bb9bb45f authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

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: a6673429 ("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: default avatarYue Sun <samsun1006219@gmail.com>
Reported-by: default avatarXingwei Lee <xrivendell7@gmail.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20240610124406.359476013@linutronix.de
parent c80c4490

arch/x86/events/core.c

+3 −0
Original line number Diff line number Diff line
@@ -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,