Patch "perf/x86: Serialize set_attr_rdpmc()" has been added to the 6.1-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    perf/x86: Serialize set_attr_rdpmc()

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     perf-x86-serialize-set_attr_rdpmc.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 91b03b8c750d9080fb278f83ddb69d04de7b4a9e
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date:   Mon Jun 10 14:46:35 2024 +0200

    perf/x86: Serialize set_attr_rdpmc()
    
    [ Upstream commit 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: 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@xxxxxxxxxxxxxx
    Reported-by: Yue Sun <samsun1006219@xxxxxxxxx>
    Reported-by: Xingwei Lee <xrivendell7@xxxxxxxxx>
    Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Link: https://lkml.kernel.org/r/20240610124406.359476013@xxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 1394312b732a3..2b2c9fd74ef90 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2573,6 +2573,7 @@ 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;
 
@@ -2586,6 +2587,8 @@ 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,