Patch "sched/core: Fix incorrect initialization of the 'burst' parameter in cpu_max_write()" has been added to the 6.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    sched/core: Fix incorrect initialization of the 'burst' parameter in cpu_max_write()

to the 6.9-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:
     sched-core-fix-incorrect-initialization-of-the-burst.patch
and it can be found in the queue-6.9 subdirectory.

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



commit 010193805ad93b1e93b56ede52655b95b80fbb26
Author: Cheng Yu <serein.chengyu@xxxxxxxxxx>
Date:   Wed Apr 24 21:24:38 2024 +0800

    sched/core: Fix incorrect initialization of the 'burst' parameter in cpu_max_write()
    
    [ Upstream commit 49217ea147df7647cb89161b805c797487783fc0 ]
    
    In the cgroup v2 CPU subsystem, assuming we have a
    cgroup named 'test', and we set cpu.max and cpu.max.burst:
    
        # echo 1000000 > /sys/fs/cgroup/test/cpu.max
        # echo 1000000 > /sys/fs/cgroup/test/cpu.max.burst
    
    then we check cpu.max and cpu.max.burst:
    
        # cat /sys/fs/cgroup/test/cpu.max
        1000000 100000
        # cat /sys/fs/cgroup/test/cpu.max.burst
        1000000
    
    Next we set cpu.max again and check cpu.max and
    cpu.max.burst:
    
        # echo 2000000 > /sys/fs/cgroup/test/cpu.max
        # cat /sys/fs/cgroup/test/cpu.max
        2000000 100000
    
        # cat /sys/fs/cgroup/test/cpu.max.burst
        1000
    
    ... we find that the cpu.max.burst value changed unexpectedly.
    
    In cpu_max_write(), the unit of the burst value returned
    by tg_get_cfs_burst() is microseconds, while in cpu_max_write(),
    the burst unit used for calculation should be nanoseconds,
    which leads to the bug.
    
    To fix it, get the burst value directly from tg->cfs_bandwidth.burst.
    
    Fixes: f4183717b370 ("sched/fair: Introduce the burstable CFS controller")
    Reported-by: Qixin Liao <liaoqixin@xxxxxxxxxx>
    Signed-off-by: Cheng Yu <serein.chengyu@xxxxxxxxxx>
    Signed-off-by: Zhang Qiao <zhangqiao22@xxxxxxxxxx>
    Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
    Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
    Tested-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240424132438.514720-1-serein.chengyu@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7019a40457a6d..d211d40a2edc9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11402,7 +11402,7 @@ static ssize_t cpu_max_write(struct kernfs_open_file *of,
 {
 	struct task_group *tg = css_tg(of_css(of));
 	u64 period = tg_get_cfs_period(tg);
-	u64 burst = tg_get_cfs_burst(tg);
+	u64 burst = tg->cfs_bandwidth.burst;
 	u64 quota;
 	int ret;