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

["tip-bot2 for Cheng Yu" <tip-bot2@xxxxxxxxxxxxx>]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     49217ea147df7647cb89161b805c797487783fc0
Gitweb:        https://git.kernel.org/tip/49217ea147df7647cb89161b805c797487783fc0
Author:        Cheng Yu <serein.chengyu@xxxxxxxxxx>
AuthorDate:    Wed, 24 Apr 2024 21:24:38 +08:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 17 May 2024 09:53:54 +02:00

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: 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
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1a91438..f88f505 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;