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perf/x86: Serialize set_attr_rdpmc()

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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
This commit is contained in:
Thomas Gleixner 2024-06-10 14:46:35 +02:00 committed by Peter Zijlstra
parent c80c4490c2
commit bb9bb45f74
1 changed files with 3 additions and 0 deletions
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3
arch/x86/events/core.c
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@ -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,