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

JIRA: https://issues.redhat.com/browse/RHEL-48226

commit 49217ea
Author: Cheng Yu <serein.chengyu@huawei.com>
Date:   Wed Apr 24 21:24:38 2024 +0800

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

    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: f418371 ("sched/fair: Introduce the burstable CFS controller")
    Reported-by: Qixin Liao <liaoqixin@huawei.com>
    Signed-off-by: Cheng Yu <serein.chengyu@huawei.com>
    Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
    Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
    Link: https://lore.kernel.org/r/20240424132438.514720-1-serein.chengyu@huawei.com

Signed-off-by: Phil Auld <pauld@redhat.com>

Author: auldp

kernel/sched/core.c

@@ -11506,7 +11506,7 @@ 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;