Re: [External] Re: [PATCH v2 1/2] sched/core: Fixed missing rq clock update before calling set_rq_offline()

From: Hao Jia
Date: Thu May 11 2023 - 00:05:35 EST

Next message: Al Viro: "Re: [PATCH] uacce: use filep->f_mapping to replace inode->i_mapping"
Previous message: Michael Shavit: "Re: [PATCH v1 0/5] Add PASID support to SMMUv3 unmanaged domains"
In reply to: Peter Zijlstra: "Re: [PATCH v2 1/2] sched/core: Fixed missing rq clock update before calling set_rq_offline()"
Next in thread: Hao Jia: "[PATCH v2 2/2] sched/core: Avoid double calling update_rq_clock()"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

On 2023/5/10 Peter Zijlstra wrote:

On Wed, May 10, 2023 at 04:34:49PM +0800, Hao Jia wrote:

This is triggered during cpu offline when CONFIG_CPU_FREQ is enabled:

I'm failing to see the relevance to CPU_FREQ...

Sorry to confuse you, here is a more detailed function call graph.

rq_offline_rt()
__disable_runtime()
sched_rt_rq_enqueue()
enqueue_top_rt_rq()
cpufreq_update_util() <-- depends on CONFIG_CPU_FREQ
data->func(data, *rq_clock(rq)*, flags);
intel_pstate_update_util() <-- on my machine, I have set cpufreq to powersave

Perhaps we need to add the above information to the commit Changelog?

------------[ cut here ]------------
rq->clock_update_flags < RQCF_ACT_SKIP
WARNING: CPU: 24 PID: 754 at kernel/sched/sched.h:1496
enqueue_top_rt_rq+0x139/0x160
Call Trace:
<TASK>
? intel_pstate_update_util+0x3b0/0x3b0

AFAICT this is __disable_runtime() re-queueing throttled RT tasks

Your unwind is dodgy, what CONFIG_UNWINDER do you have?

CONFIG_UNWINDER_ORC=y
# CONFIG_UNWINDER_FRAME_POINTER is not set

I try to use another configuration:

# CONFIG_UNWINDER_ORC is not set
CONFIG_UNWINDER_FRAME_POINTER=y

The log is as follows

[ 217.332774] ------------[ cut here ]------------
[ 217.332780] rq->clock_update_flags < RQCF_ACT_SKIP
[ 217.332788] WARNING: CPU: 0 PID: 817 at kernel/sched/sched.h:1496 enqueue_top_rt_rq+0x135/0x150

[ 217.333049] CPU: 0 PID: 817 Comm: kworker/53:1 Kdump: loaded Tainted: G S E 6.4.0-rc1.bm.1-amd64+ #73
[ 217.333056] Hardware name: FOXCONN R-5111/GROOT, BIOS IC1B123F 07/16/2020
[ 217.333060] Workqueue: events cpuset_hotplug_workfn
[ 217.333070] RIP: 0010:enqueue_top_rt_rq+0x135/0x150
[ 217.333078] Code: 98 00 00 00 01 00 00 00 eb 83 80 3d d0 b5 69 01 00 0f 85 3f ff ff ff 48 c7 c7 e0 39 2f 9c c6 05 bc b5 69 01 01 e8 0b 7f fa ff <0f> 0b e9 25 ff ff ff e8 7f 74 07 00 44 8b a3 30 08 00 00 e9 54 ff
[ 217.333084] RSP: 0018:ffffa7c15b94fac0 EFLAGS: 00010086
[ 217.333090] RAX: 0000000000000000 RBX: ffff93ad006ef580 RCX: 0000000000000003
[ 217.333094] RDX: 0000000000000003 RSI: ffffffff9c32eab9 RDI: 00000000ffffffff
[ 217.333097] RBP: ffffa7c15b94fad8 R08: 0000000000000000 R09: c0000000ffffbfff
[ 217.333101] R10: ffffa7c15b94f9b8 R11: ffffa7c15b94f908 R12: ffff934f52166608
[ 217.333104] R13: ffffffff9baff3c0 R14: 0000000000000246 R15: ffff93ad006ef340
[ 217.333107] FS: 0000000000000000(0000) GS:ffff93ad00600000(0000) knlGS:0000000000000000
[ 217.333112] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 217.333115] CR2: 00007f7d2ffa6ba0 CR3: 000000604df16003 CR4: 00000000007706f0
[ 217.333119] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 217.333122] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 217.333125] PKRU: 55555554
[ 217.333128] Call Trace:
[ 217.333131] <TASK>
[ 217.333136] rq_offline_rt+0x1b8/0x250
[ 217.333146] set_rq_offline.part.121+0x2d/0x70
[ 217.333159] set_rq_offline+0x18/0x20
[ 217.333165] rq_attach_root+0xcf/0xe0
[ 217.333176] cpu_attach_domain+0x3cb/0x7d0
[ 217.333186] partition_sched_domains_locked+0x2a4/0x3b0
[ 217.333197] rebuild_sched_domains_locked+0x47e/0x800
[ 217.333202] ? preempt_schedule_common+0x37/0x90
[ 217.333213] rebuild_sched_domains+0x1f/0x40
[ 217.333218] cpuset_hotplug_workfn+0x2df/0xd10
[ 217.333225] ? debug_smp_processor_id+0x17/0x20
[ 217.333233] ? _raw_spin_unlock+0x19/0x30
[ 217.333242] ? raw_spin_rq_unlock+0x10/0x30
[ 217.333247] ? finish_task_switch+0x98/0x2f0
[ 217.333251] ? __switch_to+0x12b/0x440
[ 217.333261] ? __switch_to_asm+0x34/0x60
[ 217.333270] ? __schedule+0x600/0x14e0
[ 217.333276] ? __queue_delayed_work+0x8b/0x90
[ 217.333285] ? queue_delayed_work_on+0x3a/0x50
[ 217.333291] process_one_work+0x1c8/0x3e0
[ 217.333298] worker_thread+0x4d/0x390
[ 217.333305] ? rescuer_thread+0x350/0x350
[ 217.333311] kthread+0xfe/0x130
[ 217.333316] ? kthread_complete_and_exit+0x20/0x20
[ 217.333321] ret_from_fork+0x1f/0x30
[ 217.333331] </TASK>
[ 217.333333] ---[ end trace 0000000000000000 ]---

Tests are done in an Intel Xeon(R) Platinum 8260 CPU@2.40GHz machine
with 2 NUMA nodes each of which has 24 cores with SMT2 enabled, so 96
CPUs in total.

rq_offline_rt+0x1b7/0x250
set_rq_offline.part.120+0x28/0x60
rq_attach_root+0xc4/0xd0
cpu_attach_domain+0x3dc/0x7f0
? __schedule+0x65e/0x1310
partition_sched_domains_locked+0x2a5/0x3c0
rebuild_sched_domains_locked+0x477/0x830
? percpu_rwsem_wait+0x140/0x140
rebuild_sched_domains+0x1b/0x30
cpuset_hotplug_workfn+0x2ca/0xc90
? balance_push+0x56/0x120
? _raw_spin_unlock+0x15/0x30
? finish_task_switch+0x98/0x2f0
? __switch_to+0x116/0x410
? __schedule+0x65e/0x1310 ? internal_add_timer+0x42/0x60
? _raw_spin_unlock_irqrestore+0x23/0x40
? add_timer_on+0xd5/0x130
process_one_work+0x1bc/0x3d0
worker_thread+0x4c/0x380
? preempt_count_add+0x56/0xa0
? rescuer_thread+0x310/0x310
kthread+0xe6/0x110
? kthread_complete_and_exit+0x20/0x20
ret_from_fork+0x1f/0x30

Before calling set_rq_offline() we need to update the rq clock to avoid
using the old rq clock, and use rq_lock_irqsave()/rq_unlock_irqrestore()
to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore() to
ensure that rq->clock_update_flags are cleared before updating the rq
clock.

Steps to reproduce:
1. Enable CONFIG_SMP and CONFIG_CPU_FREQ when compiling the kernel
2. echo 1 > /sys/kernel/debug/clear_warn_once
3. cpupower -c all frequency-set -g powersave
4. Run some rt tasks e.g. Create 5*n rt (100% running) tasks (on a
system with n CPUs)
5. Offline cpu one by one until the warninng is triggered

Signed-off-by: Hao Jia <jiahao.os@xxxxxxxxxxxxx>
---
kernel/sched/topology.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 6682535e37c8..b89497696880 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -487,15 +487,17 @@ static void free_rootdomain(struct rcu_head *rcu)
void rq_attach_root(struct rq *rq, struct root_domain *rd)
{
struct root_domain *old_rd = NULL;
- unsigned long flags;
+ struct rq_flags rf;
- raw_spin_rq_lock_irqsave(rq, flags);
+ rq_lock_irqsave(rq, &rf);
if (rq->rd) {
old_rd = rq->rd;
- if (cpumask_test_cpu(rq->cpu, old_rd->online))
+ if (cpumask_test_cpu(rq->cpu, old_rd->online)) {
+ update_rq_clock(rq);
set_rq_offline(rq);
+ }
cpumask_clear_cpu(rq->cpu, old_rd->span);
@@ -515,7 +517,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
set_rq_online(rq);
- raw_spin_rq_unlock_irqrestore(rq, flags);
+ rq_unlock_irqrestore(rq, &rf);
if (old_rd)
call_rcu(&old_rd->rcu, free_rootdomain);

The patch itself is good though; just the Changelog has me
confused.

Sorry for not explaining clearly and confusing you.

Thanks,
Hao

Next message: Al Viro: "Re: [PATCH] uacce: use filep->f_mapping to replace inode->i_mapping"
Previous message: Michael Shavit: "Re: [PATCH v1 0/5] Add PASID support to SMMUv3 unmanaged domains"
In reply to: Peter Zijlstra: "Re: [PATCH v2 1/2] sched/core: Fixed missing rq clock update before calling set_rq_offline()"
Next in thread: Hao Jia: "[PATCH v2 2/2] sched/core: Avoid double calling update_rq_clock()"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]