Commit 4b1bd46a authored Sep 25, 2024 by Thomas Gleixner Committed by Luo Gengkun Sep 25, 2024

perf/x86: Serialize set_attr_rdpmc()

mainline inclusion
from mainline-v6.11-rc1
commit bb9bb45f746b0f9457de9c3fc4da143a6351bdc9
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/IAMTVO

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bb9bb45f746b0f9457de9c3fc4da143a6351bdc9

--------------------------------

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: 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


Conflicts:
	arch/x86/events/core.c
[Using mutex_lock/mutex_unlock instead of guard]
Signed-off-by: Luo Gengkun <luogengkun2@huawei.com>

parent d831c8e9

arch/x86/events/core.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -2529,6 +2529,7 @@ 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;

		@@ -2542,6 +2543,8 @@ static ssize_t set_attr_rdpmc(struct device *cdev,
		if (x86_pmu.attr_rdpmc_broken)
		return -ENOTSUPP;

		mutex_lock(&rdpmc_mutex);

		if (val != x86_pmu.attr_rdpmc) {
		/*
		* Changing into or out of never available or always available,
		@@ -2562,6 +2565,8 @@ static ssize_t set_attr_rdpmc(struct device *cdev,
		x86_pmu.attr_rdpmc = val;
		}

		mutex_unlock(&rdpmc_mutex);

		return count;
		}