The commit 851a723e45d1c("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()")
would cause that online/offline cpu will produce different results
for the !top-cpuset task.
For example:
If the task was running, then offline task's cpus, would lead to clear
its user-mask.
unisoc:/ # while true; do sleep 600; done&
[1] 6786
unisoc:/ # echo 6786 > /dev/cpuset/top-app/tasks
unisoc:/ # cat /dev/cpuset/top-app/cpus
0-7
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: ff
Cpus_allowed_list: 0-7
unisoc:/ # taskset -p c0 6786
pid 6786's current affinity mask: ff
pid 6786's new affinity mask: c0
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: c0
Cpus_allowed_list: 6-7
After offline the cpu6 and cpu7, the user-mask would be cleared:
unisoc:/ # echo 0 > /sys/devices/system/cpu/cpu7/online
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: 40
Cpus_allowed_list: 6
ums9621_1h10:/ # echo 0 > /sys/devices/system/cpu/cpu6/online
ums9621_1h10:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: 3f
Cpus_allowed_list: 0-5
When online the cpu6/7, the user-mask can not bring back:
unisoc:/ # echo 1 > /sys/devices/system/cpu/cpu6/online
unisoc:/ # echo 1 > /sys/devices/system/cpu/cpu7/online
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: ff
Cpus_allowed_list: 0-6
However, if we offline the cpu when the task is sleeping, at this
time, because would not call the fallback_cpu(), its user-mask will
not be cleared.
unisoc:/ # while true; do sleep 600; done&
[1] 5990
unisoc:/ # echo 5990 > /dev/cpuset/top-app/tasks
unisoc:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: ff
Cpus_allowed_list: 0-7
unisoc:/ # taskset -p c0 5990
pid 5990's current affinity mask: ff
pid 5990's new affinity mask: c0
unisoc:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: c0
Cpus_allowed_list: 6-7
unisoc:/ # echo 0 > /sys/devices/system/cpu/cpu6/online
unisoc:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: 80
Cpus_allowed_list: 7
unisoc:/ # echo 0 > /sys/devices/system/cpu/cpu7/online
unisoc:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: 3f
Cpus_allowed_list: 0-5
After 10 minutes, it was waked up, it can also keep its user-mask:
ums9621_1h10:/ # cat /proc/5990/status | grep Cpus
Cpus_allowed: 3f
Cpus_allowed_list: 0-5
And when online the cpu6/7,the user-mask could bring back.
unisoc:/ # echo 1 > /sys/devices/system/cpu/cpu6/online
unisoc:/ # echo 1 > /sys/devices/system/cpu/cpu7/online
unisoc:/ # cat /proc/6786/status | grep Cpus
Cpus_allowed: c0
Cpus_allowed_list: 6-7
Indeed, there is no need to clear the user_cpus_ptr if there is an
intersection between user_cpus_ptr and new_mask.
So add the judgement of whether there is an intersection between them.
Clear user_cpus_ptr only when no intersection with the new mask.
In this way, the above problems can also be solved.
Suggested-by: Waiman Long <[email protected]>
Signed-off-by: Xuewen Yan <[email protected]>
---
previous discussion:
https://lore.kernel.org/all/[email protected]/
---
kernel/sched/core.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7019a40457a6..bbb8e88949f4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2796,21 +2796,24 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
}
/*
- * Used for kthread_bind() and select_fallback_rq(), in both cases the user
- * affinity (if any) should be destroyed too.
+ * Used for kthread_bind() and select_fallback_rq().
+ * Destroy user affinity if no intersection with the new_mask.
*/
void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
{
struct affinity_context ac = {
.new_mask = new_mask,
.user_mask = NULL,
- .flags = SCA_USER, /* clear the user requested mask */
+ .flags = 0,
};
union cpumask_rcuhead {
cpumask_t cpumask;
struct rcu_head rcu;
};
+ if (p->user_cpus_ptr && !cpumask_intersects(p->user_cpus_ptr, new_mask))
+ ac.flags = SCA_USER; /* clear the user requested mask */
+
__do_set_cpus_allowed(p, &ac);
/*
--
2.25.1