The commit is pushed to "branch-rh7-3.10.0-693.21.1.vz7.47.x-ovz" and will
appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.21.1.vz7.47.2
------>
commit 686f2db03b54b781ac72d93f74a49180d01cce86
Author: Kirill Tkhai <[email protected]>
Date: Fri Apr 27 13:44:36 2018 +0300
sched/rt: Stop for_each_process_thread() iterations in tg_has_rt_tasks()
tg_rt_schedulable() iterates over all child task groups,
while tg_has_rt_tasks() iterates over all linked tasks.
In case of systems with big number of tasks, this may
take a lot of time.
I observed hard LOCKUP on machine with 20000+ processes
after write to "cpu.rt_period_us" of cpu cgroup with
39 children. The problem occurred because of tasklist_lock
is held for a long time and other processes can't do fork().
PID: 1036268 TASK: ffff88766c310000 CPU: 36 COMMAND: "criu"
#0 [ffff887f7f408e48] crash_nmi_callback at ffffffff81050601
#1 [ffff887f7f408e58] nmi_handle at ffffffff816e0cc7
#2 [ffff887f7f408eb0] do_nmi at ffffffff816e0fb0
#3 [ffff887f7f408ef0] end_repeat_nmi at ffffffff816e00b9
[exception RIP: tg_rt_schedulable+463]
RIP: ffffffff810bf49f RSP: ffff886537ad7d50 RFLAGS: 00000202
RAX: 0000000000000000 RBX: 000000003b9aca00 RCX: ffff883e9cb4b1b0
RDX: ffff887d0be43608 RSI: ffff886537ad7dd8 RDI: ffff8840a6ad0000
RBP: ffff886537ad7d68 R8: ffff887d0be431b0 R9: 00000000000e7ef0
R10: ffff88164fc39400 R11: 0000000000023380 R12: ffffffff81ef8d00
R13: ffffffff810bea40 R14: 0000000000000000 R15: ffff8840a6ad0000
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
---
kernel/sched/core.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f14bbf5c8ed6..5987f85379a9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8955,17 +8955,27 @@ void sched_move_task(struct task_struct *tsk)
*/
static DEFINE_MUTEX(rt_constraints_mutex);
-/* Must be called with tasklist_lock held */
static inline int tg_has_rt_tasks(struct task_group *tg)
{
- struct task_struct *g, *p;
+ struct cgroup *cgroup;
+ struct task_struct *p;
+ struct cgroup_iter it;
+ int ret = 0;
- do_each_thread(g, p) {
- if (rt_task(p) && task_rq(p)->rt.tg == tg)
- return 1;
- } while_each_thread(g, p);
+ if (task_group_is_autogroup(tg))
+ return 0;
- return 0;
+ cgroup = tg->css.cgroup;
+
+ cgroup_iter_start(cgroup, &it);
+ while ((p = cgroup_iter_next(cgroup, &it)))
+ if (rt_task(p)) {
+ ret = 1;
+ break;
+ }
+ cgroup_iter_end(cgroup, &it);
+
+ return ret;
}
struct rt_schedulable_data {
@@ -9053,7 +9063,6 @@ static int tg_set_rt_bandwidth(struct task_group *tg,
int i, err = 0;
mutex_lock(&rt_constraints_mutex);
- qread_lock(&tasklist_lock);
err = __rt_schedulable(tg, rt_period, rt_runtime);
if (err)
goto unlock;
@@ -9071,7 +9080,6 @@ static int tg_set_rt_bandwidth(struct task_group *tg,
}
raw_spin_unlock_irq(&tg->rt_bandwidth.rt_runtime_lock);
unlock:
- qread_unlock(&tasklist_lock);
mutex_unlock(&rt_constraints_mutex);
return err;
@@ -9130,9 +9138,7 @@ static int sched_rt_global_constraints(void)
int ret = 0;
mutex_lock(&rt_constraints_mutex);
- qread_lock(&tasklist_lock);
ret = __rt_schedulable(NULL, 0, 0);
- qread_unlock(&tasklist_lock);
mutex_unlock(&rt_constraints_mutex);
return ret;
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