On 1/27/2021 5:21 PM, Hillf Danton wrote:
> On Wed, 27 Jan 2021 16:04:25 +0800 Xing Zhengjun wrote:
>> On 1/26/2021 3:39 PM, Hillf Danton wrote:
>>> On 26 Jan 2021 10:45:21 +0800 Xing Zhengjun wrote:
>>>> On 1/25/2021 5:29 PM, Hillf Danton wrote:
>>>>> On 25 Jan 2021 16:31:32 +0800 Xing Zhengjun wrote:
>>>>>> On 1/22/2021 3:59 PM, Hillf Danton wrote:
>>>>>>> On Fri, 22 Jan 2021 09:48:32 +0800 Xing Zhengjun wrote:
>>>>>>>> On 1/21/2021 12:00 PM, Hillf Danton wrote:
>>>>>>>>> On Wed, 20 Jan 2021 21:46:33 +0800 Oliver Sang wrote:
>>>>>>>>>> On Fri, Jan 15, 2021 at 03:24:32PM +0800, Hillf Danton wrote:
>>>>>>>>>>> Thu, 14 Jan 2021 15:45:11 +0800
>>>>>>>>>>>>
>>>>>>>>>>>> FYI, we noticed the following commit (built with gcc-9):
>>>>>>>>>>>>
>>>>>>>>>>>> commit: d5bff968ea9cc005e632d9369c26cbd8148c93d5 ("workqueue: break affinity initiatively")
>>>>>>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/paulmck/linux-rcu.git dev.2021.01.11b
>>>>>>>>>>>>
>>>>>>>>>>> [...]
>>>>>>>>>>>>
>>>>>>>>>>>> [ 73.794288] WARNING: CPU: 0 PID: 22 at kernel/workqueue.c:2192 process_one_work
>>>>>>>>>>>
>>>>>>>>>>> Thanks for your report.
>>>>>>>>>>>
>>>>>>>>>>> We can also break CPU affinity by checking POOL_DISASSOCIATED at attach
>>>>>>>>>>> time without extra cost paid; that way we have the same behavior as at
>>>>>>>>>>> the unbind time.
>>>>>>>>>>>
>>>>>>>>>>> What is more the change that makes kworker pcpu is cut because they are
>>>>>>>>>>> going to not help either hotplug or the mechanism of stop machine.
>>>>>>>>>>
>>>>>>>>>> hi, by applying below patch, the issue still happened.
>>>>>>>>>
>>>>>>>>> Thanks for your report.
>>>>>>>>>>
>>>>>>>>>> [ 4.574467] pci 0000:00:00.0: Limiting direct PCI/PCI transfers
>>>>>>>>>> [ 4.575651] pci 0000:00:01.0: Activating ISA DMA hang workarounds
>>>>>>>>>> [ 4.576900] pci 0000:00:02.0: Video device with shadowed ROM at [mem 0x000c0000-0x000dffff]
>>>>>>>>>> [ 4.578648] PCI: CLS 0 bytes, default 64
>>>>>>>>>> [ 4.579685] Unpacking initramfs...
>>>>>>>>>> [ 8.878031] -----------[ cut here ]-----------
>>>>>>>>>> [ 8.879083] WARNING: CPU: 0 PID: 22 at kernel/workqueue.c:2187 process_one_work+0x92/0x9e0
>>>>>>>>>> [ 8.880688] Modules linked in:
>>>>>>>>>> [ 8.881274] CPU: 0 PID: 22 Comm: kworker/1:0 Not tainted 5.11.0-rc3-gc213503139bb #2
>>>>>>>>>
>>>>>>>>> The kworker bond to CPU1 runs on CPU0 and triggers the warning, which
>>>>>>>>> shows that scheduler breaks CPU affinity, after 06249738a41a
>>>>>>>>> ("workqueue: Manually break affinity on hotplug"), though quite likely
>>>>>>>>> by kworker/1:0 for the initial workers.
>>>>>>>>>
>>>>>>>>>> [ 8.882518] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
>>>>>>>>>> [ 8.887539] Workqueue: 0x0 (events)
>>>>>>>>>> [ 8.887838] EIP: process_one_work+0x92/0x9e0
>>>>>>>>>> [ 8.887838] Code: 37 64 a1 58 54 4c 43 39 45 24 74 2c 31 c9 ba 01 00 00 00 c7 04 24 01 00 00 00 b8 08 1d f5 42 e8 74 85 13 00 ff 05 b8 30 04 43 <0f> 0b ba 01 00 00 00 eb 22 8d 74 26 00 90 c7 04 24 01 00 00 00 31
>>>>>>>>>> [ 8.887838] EAX: 42f51d08 EBX: 00000000 ECX: 00000000 EDX: 00000001
>>>>>>>>>> [ 8.887838] ESI: 43c04720 EDI: 42e45620 EBP: de7f23c0 ESP: 43d7bf08
>>>>>>>>>> [ 8.887838] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010002
>>>>>>>>>> [ 8.887838] CR0: 80050033 CR2: 00000000 CR3: 034e3000 CR4: 000406d0
>>>>>>>>>> [ 8.887838] Call Trace:
>>>>>>>>>> [ 8.887838] ? worker_thread+0x98/0x6a0
>>>>>>>>>> [ 8.887838] ? worker_thread+0x2dd/0x6a0
>>>>>>>>>> [ 8.887838] ? kthread+0x1ba/0x1e0
>>>>>>>>>> [ 8.887838] ? create_worker+0x1e0/0x1e0
>>>>>>>>>> [ 8.887838] ? kzalloc+0x20/0x20
>>>>>>>>>> [ 8.887838] ? ret_from_fork+0x1c/0x28
>>>>>>>>>> [ 8.887838] _warn_unseeded_randomness: 63 callbacks suppressed
>>>>>>>>>> [ 8.887838] random: get_random_bytes called from init_oops_id+0x2b/0x60 with crng_init=0
>>>>>>>>>> [ 8.887838] --[ end trace ac461b4d54c37cfa ]--
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Instead of creating the initial workers only on the active CPUS, rebind
>>>>>>>>> them (labeled pcpu) and jump to the right CPU at bootup time.
>>>>>>>>>
>>>>>>>>> --- a/kernel/workqueue.c
>>>>>>>>> +++ b/kernel/workqueue.c
>>>>>>>>> @@ -2385,6 +2385,16 @@ woke_up:
>>>>>>>>> return 0;
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> + if (!(pool->flags & POOL_DISASSOCIATED) && smp_processor_id() !=
>>>>>>>>> + pool->cpu) {
>>>>>>>>> + /* scheduler breaks CPU affinity for us, rebind it */
>>>>>>>>> + raw_spin_unlock_irq(&pool->lock);
>>>>>>>>> + set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
>>>>>>>>> + /* and jump to the right seat */
>>>>>>>>> + schedule_timeout_interruptible(1);
>>>>>>>>> + goto woke_up;
>>>>>>>>> + }
>>>>>>>>> +
>>>>>>>>> worker_leave_idle(worker);
>>>>>>>>> recheck:
>>>>>>>>> /* no more worker necessary? */
>>>>>>>>> --
>>>>>>>>>
>>>>>>>> I test the patch, the warning still appears in the kernel log.
>>>>>>>
>>>>>>> Thanks for your report.
>>>>>>>>
>>>>>>>> [ 230.356503] smpboot: CPU 1 is now offline
>>>>>>>> [ 230.544652] x86: Booting SMP configuration:
>>>>>>>> [ 230.545077] smpboot: Booting Node 0 Processor 1 APIC 0x1
>>>>>>>> [ 230.545640] kvm-clock: cpu 1, msr 34f6021, secondary cpu clock
>>>>>>>> [ 230.545675] masked ExtINT on CPU#1
>>>>>>>> [ 230.593829] ------------[ cut here ]------------
>>>>>>>> [ 230.594257] WARNING: CPU: 0 PID: 257 at kernel/workqueue.c:2192 process_one_work+0x92/0x9e0
>>>>>>>> [ 230.594990] Modules linked in: rcutorture torture mousedev input_leds
>>>>>>>> led_class pcspkr psmouse evbug tiny_power_button button
>>>>>>>> [ 230.595961] CPU: 0 PID: 257 Comm: kworker/1:3 Not tainted 5.11.0-rc3-gdcba55d9080f #2
>>>>>>>
>>>>>>> Like what was reported, kworker bond to CPU1 runs on CPU0 and triggers
>>>>>>> warning, due to scheduler breaking CPU affinity for us. What is new, the
>>>>>>> affinity was broken at offline time instead of bootup.
>>>>>>>
>>>>>>>> [ 230.596621] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
>>>>>>>> [ 230.597322] Workqueue: 0x0 (rcu_gp)
>>>>>>>> [ 230.597636] EIP: process_one_work+0x92/0x9e0
>>>>>>>> [ 230.598005] Code: 37 64 a1 58 54 4c 43 39 45 24 74 2c 31 c9 ba 01 00
>>>>>>>> 00 00 c7 04 24 01 00 00 00 b8 08 1d f5 42 e8 f4 85 13 00 ff 05 cc 30 04
>>>>>>>> 43 <0f> 0b ba 01 00 00 00 eb 22 8d 74 26 00 90 c7 04 24 01 00 00 00 31
>>>>>>>> [ 230.599569] EAX: 42f51d08 EBX: 00000000 ECX: 00000000 EDX: 00000001
>>>>>>>> [ 230.600100] ESI: 43d94240 EDI: df4040f4 EBP: de7f23c0 ESP: bf5f1f08
>>>>>>>> [ 230.600629] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010002
>>>>>>>> [ 230.601203] CR0: 80050033 CR2: 01bdecbc CR3: 04e2c000 CR4: 000406d0
>>>>>>>> [ 230.601735] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
>>>>>>>> [ 230.602265] DR6: fffe0ff0 DR7: 00000400
>>>>>>>> [ 230.602594] Call Trace:
>>>>>>>> [ 230.602813] ? process_one_work+0x20e/0x9e0
>>>>>>>> [ 230.603181] ? worker_thread+0x32d/0x700
>>>>>>>> [ 230.603522] ? kthread+0x1ba/0x1e0
>>>>>>>> [ 230.603818] ? create_worker+0x1e0/0x1e0
>>>>>>>> [ 230.604157] ? kzalloc+0x20/0x20
>>>>>>>> [ 230.604524] ? ret_from_fork+0x1c/0x28
>>>>>>>> [ 230.604850] ---[ end trace 06b1e66b5e17fa85 ]---
>>>>>>>> [ 230.605504] kvm-guest: stealtime: cpu 1, msr 9e7e6ec0
>>>>>>>> [ 230.766960] smpboot: CPU 1 is now offline
>>>>>>>> [ 230.814803] x86: Booting SMP configuration:
>>>>>>>> [ 230.815306] smpboot: Booting Node 0 Processor 1 APIC 0x1
>>>>>>>> [ 230.815964] kvm-clock: cpu 1, msr 34f6021, secondary cpu clock
>>>>>>>
>>>>>>>
>>>>>>> Unlike the above diff that is at most papering over the problem
>>>>>>> sitting somewhere in the scheduler, add change to creating worker
>>>>>>> by skipping set_cpus_allowed_ptr() because we will wake it up after
>>>>>>> attaching it to worker pool.
>>>>>>>
>>>>>>> If we can ignore rescuer for now, then the allowed ptr is only
>>>>>>> updated at on/offline time; lets see the difference at boot time.
>>>>>>>
>>>>>>>
>>>>>>> --- a/kernel/workqueue.c
>>>>>>> +++ b/kernel/workqueue.c
>>>>>>> @@ -1844,16 +1844,10 @@ static struct worker *alloc_worker(int n
>>>>>>> * cpu-[un]hotplugs.
>>>>>>> */
>>>>>>> static void worker_attach_to_pool(struct worker *worker,
>>>>>>> - struct worker_pool *pool)
>>>>>>> + struct worker_pool *pool,
>>>>>>> + int update_cpus_allowed)
>>>>>>> {
>>>>>>> mutex_lock(&wq_pool_attach_mutex);
>>>>>>> -
>>>>>>> - /*
>>>>>>> - * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
>>>>>>> - * online CPUs. It'll be re-applied when any of the CPUs come up.
>>>>>>> - */
>>>>>>> - set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
>>>>>>> -
>>>>>>> /*
>>>>>>> * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
>>>>>>> * stable across this function. See the comments above the flag
>>>>>>> @@ -1867,6 +1861,9 @@ static void worker_attach_to_pool(struct
>>>>>>> list_add_tail(&worker->node, &pool->workers);
>>>>>>> worker->pool = pool;
>>>>>>>
>>>>>>> + if (update_cpus_allowed)
>>>>>>> + set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
>>>>>>> +
>>>>>>> mutex_unlock(&wq_pool_attach_mutex);
>>>>>>> }
>>>>>>>
>>>>>>> @@ -1942,8 +1939,11 @@ static struct worker *create_worker(stru
>>>>>>> set_user_nice(worker->task, pool->attrs->nice);
>>>>>>> kthread_bind_mask(worker->task, pool->attrs->cpumask);
>>>>>>>
>>>>>>> - /* successful, attach the worker to the pool */
>>>>>>> - worker_attach_to_pool(worker, pool);
>>>>>>> + /*
>>>>>>> + * attach the worker to the pool without asking scheduler to
>>>>>>> + * update CPUs allowed
>>>>>>> + */
>>>>>>> + worker_attach_to_pool(worker, pool, 0);
>>>>>>>
>>>>>>> /* start the newly created worker */
>>>>>>> raw_spin_lock_irq(&pool->lock);
>>>>>>> @@ -2508,7 +2508,7 @@ repeat:
>>>>>>>
>>>>>>> raw_spin_unlock_irq(&wq_mayday_lock);
>>>>>>>
>>>>>>> - worker_attach_to_pool(rescuer, pool);
>>>>>>> + worker_attach_to_pool(rescuer, pool, 1);
>>>>>>>
>>>>>>> raw_spin_lock_irq(&pool->lock);
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>> I test the patch, the warning still appears in the kernel log.
>>>>>
>>>>> Thanks.
>>>>>>
>>>>>> [ 55.754187] smpboot: Booting Node 0 Processor 1 APIC 0x1
>>>>>> [ 55.785594] kvm-clock: cpu 1, msr 34f6021, secondary cpu clock
>>>>>> [ 55.785646] masked ExtINT on CPU#1
>>>>>> [ 55.920602] ------------[ cut here ]------------
>>>>>> [ 55.921355] WARNING: CPU: 0 PID: 160 at kernel/workqueue.c:2192 process_one_work+0x92/0x9e0
>>>>>> [ 55.922583] Modules linked in: rcutorture torture mousedev evbug
>>>>>> input_leds led_class tiny_power_button psmouse pcspkr button
>>>>>> [ 55.924294] CPU: 0 PID: 160 Comm: kworker/1:2 Not tainted 5.11.0-rc3-00186-g77bf4e461cfa #2
>>>>>
>>>>> Same issue as before.
>>>>>
>>>>>> [ 55.925552] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
>>>>>> [ 55.926763] Workqueue: 0x0 (rcu_gp)
>>>>>> [ 55.927298] EIP: process_one_work+0x92/0x9e0
>>>>>> [ 55.927950] Code: 37 64 a1 58 54 4c 43 39 45 24 74 2c 31 c9 ba 01 00
>>>>>> 00 00 c7 04 24 01 00 00 00 b8 08 1d f5 42 e8 94 85 13 00 ff 05 b8 30 04
>>>>>> 43 <0f> 0b ba 01 00 00 00 eb 22 8d 74 26 00 90 c7 04 24 01 00 00 00 31
>>>>>> [ 55.930726] EAX: 42f51d08 EBX: 00000000 ECX: 00000000 EDX: 00000001
>>>>>> [ 55.931642] ESI: 43d90540 EDI: df48c0f4 EBP: de7f23c0 ESP: bfb47f08
>>>>>> [ 55.932590] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010002
>>>>>> [ 55.933609] CR0: 80050033 CR2: 024e994c CR3: 7fd80000 CR4: 000406d0
>>>>>> [ 55.934555] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
>>>>>> [ 55.935457] DR6: fffe0ff0 DR7: 00000400
>>>>>> [ 55.936041] Call Trace:
>>>>>> [ 55.936534] ? process_one_work+0x20e/0x9e0
>>>>>> [ 55.937305] ? worker_thread+0x2dd/0x6a0
>>>>>> [ 55.938018] ? kthread+0x1ba/0x1e0
>>>>>> [ 55.938598] ? create_worker+0x1e0/0x1e0
>>>>>> [ 55.939315] ? kzalloc+0x20/0x20
>>>>>> [ 55.940000] ? ret_from_fork+0x1c/0x28
>>>>>> [ 55.940627] ---[ end trace d155e9e6402de179 ]---
>>>>>> [ 55.941641] kvm-guest: stealtime: cpu 1, msr 9e7e6ec0
>>>>>> [ 56.155271] smpboot: CPU 1 is now offline
>>>>>> [ 56.193613] x86: Booting SMP configuration:
>>>>>> [ 56.194400] smpboot: Booting Node 0 Processor 1 APIC 0x1
>>>>>
>>>>> The changes in the diff below are
>>>>>
>>>>> 1/ at rescue time, change CPU affinity only if POOL_DISASSOCIATED
>>>>> is not set, and print warning the same way as offline time.
>>>>>
>>>>> 2/ at offine time, dont update allowed CPUs after setting
>>>>> POOL_DISASSOCIATED because we no longer have interest in affinity.
>>>>>
>>>>> 3/ at online time, mark pcpu before binding affinity.
>>>>>
>>>>> Though one change a diff is appreciated, by the WARNs, we can tell
>>>>> which is what if any warning goes into dmesg.
>>>>>
>>>>> --- a/kernel/workqueue.c
>>>>> +++ b/kernel/workqueue.c
>>>>> @@ -1844,25 +1844,23 @@ static struct worker *alloc_worker(int n
>>>>> * cpu-[un]hotplugs.
>>>>> */
>>>>> static void worker_attach_to_pool(struct worker *worker,
>>>>> - struct worker_pool *pool)
>>>>> + struct worker_pool *pool, int set)
>>>>> {
>>>>> mutex_lock(&wq_pool_attach_mutex);
>>>>>
>>>>> /*
>>>>> - * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
>>>>> - * online CPUs. It'll be re-applied when any of the CPUs come up.
>>>>> - */
>>>>> - set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
>>>>> -
>>>>> - /*
>>>>> * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
>>>>> * stable across this function. See the comments above the flag
>>>>> * definition for details.
>>>>> */
>>>>> if (pool->flags & POOL_DISASSOCIATED)
>>>>> worker->flags |= WORKER_UNBOUND;
>>>>> - else
>>>>> + else {
>>>>> kthread_set_per_cpu(worker->task, true);
>>>>> + if (set)
>>>>> + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
>>>>> + pool->attrs->cpumask) < 0);
>>>>> + }
>>>>>
>>>>> list_add_tail(&worker->node, &pool->workers);
>>>>> worker->pool = pool;
>>>>> @@ -1943,7 +1941,7 @@ static struct worker *create_worker(stru
>>>>> kthread_bind_mask(worker->task, pool->attrs->cpumask);
>>>>>
>>>>> /* successful, attach the worker to the pool */
>>>>> - worker_attach_to_pool(worker, pool);
>>>>> + worker_attach_to_pool(worker, pool, 0);
>>>>>
>>>>> /* start the newly created worker */
>>>>> raw_spin_lock_irq(&pool->lock);
>>>>> @@ -2508,7 +2506,7 @@ repeat:
>>>>>
>>>>> raw_spin_unlock_irq(&wq_mayday_lock);
>>>>>
>>>>> - worker_attach_to_pool(rescuer, pool);
>>>>> + worker_attach_to_pool(rescuer, pool, 1);
>>>>>
>>>>> raw_spin_lock_irq(&pool->lock);
>>>>>
>>>>> @@ -4923,7 +4921,6 @@ static void unbind_workers(int cpu)
>>>>>
>>>>> for_each_pool_worker(worker, pool) {
>>>>> kthread_set_per_cpu(worker->task, false);
>>>>> - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
>>>>> }
>>>>>
>>>>> mutex_unlock(&wq_pool_attach_mutex);
>>>>> @@ -4977,9 +4974,9 @@ static void rebind_workers(struct worker
>>>>> * from CPU_ONLINE, the following shouldn't fail.
>>>>> */
>>>>> for_each_pool_worker(worker, pool) {
>>>>> + kthread_set_per_cpu(worker->task, true);
>>>>> WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
>>>>> pool->attrs->cpumask) < 0);
>>>>> - kthread_set_per_cpu(worker->task, true);
>>>>> }
>>>>>
>>>>> raw_spin_lock_irq(&pool->lock);
>>>>> --
>>>>>
>>>> I test the patch, the warning still appears in the kernel log, but the
>>>
>>> Thanks.
>>>
>>>> warning is different from before.
>>>>
>>>> [ 0.054803] kvm-clock: cpu 1, msr 34f6021, secondary cpu clock
>>>> [ 0.054803] masked ExtINT on CPU#1
>>>> [ 0.054803] smpboot: CPU 1 Converting physical 0 to logical die 1
>>>> [ 1.890338] ------------[ cut here ]------------
>>>> [ 1.890338] WARNING: CPU: 1 PID: 18 at kernel/kthread.c:508 kthread_set_per_cpu+0x156/0x180
>>>> [ 1.890338] Modules linked in:
>>>> [ 1.890338] CPU: 1 PID: 18 Comm: cpuhp/1 Not tainted 5.11.0-rc3-00186-ged03082352b2 #2
>>>
>>> This warning is better than the one in process_one_work() which is too
>>> late, though, it has something to say.
>>>
>>>> [ 1.890338] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
>>>> [ 1.890338] EIP: kthread_set_per_cpu+0x156/0x180
>>>> [ 1.890338] Code: 00 00 00 00 ff 05 68 4e 04 43 83 c4 08 5b 5e 5f c3
>>>> 8d 76 00 ff 05 34 50 04 43 0f 0b e9 f9 fe ff ff 8d 76 00 ff 05 2c 4e 04
>>>> 43 <0f> 0b eb 9d 8d b6 00 00 00 00 ff 05 40 4e 04 43 0f 0b e9 45 ff ff
>>>> [ 1.890338] EAX: 42f52ce0 EBX: 00000001 ECX: 00000000 EDX: 00000001
>>>> [ 1.890338] ESI: 43d76300 EDI: 43c0de00 EBP: de7f2564 ESP: 43d6beb8
>>>> [ 1.900350] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010202
>>>> [ 1.901303] CR0: 80050033 CR2: 00000000 CR3: 034e3000 CR4: 000406d0
>>>> [ 1.902280] Call Trace:
>>>> [ 1.902682] ? workqueue_online_cpu+0x12b/0x640
>>>> [ 1.903415] ? workqueue_prepare_cpu+0xa0/0xa0
>>>
>>> By the prepare function we know it is a warning at boot time.
>>>
>>>> [ 1.904155] ? cpuhp_invoke_callback+0x1ed/0x1340
>>>> [ 1.904941] ? cpuhp_thread_fun+0x28f/0x460
>>>> [ 1.905630] ? cpuhp_thread_fun+0x49/0x460
>>>> [ 1.906298] ? smpboot_thread_fn+0x446/0x620
>>>> [ 1.910275] ? kthread+0x1ba/0x1e0
>>>> [ 1.910857] ? __smpboot_create_thread+0x260/0x260
>>>> [ 1.911659] ? kzalloc+0x20/0x20
>>>> [ 1.912368] ? ret_from_fork+0x1c/0x28
>>>> [ 1.913016] ---[ end trace 6f6c005278241eba ]---
>>>> [ 1.913971] kvm-guest: stealtime: cpu 1, msr 9e7e6ec0
>>>> [ 1.920012] smp: Brought up 1 node, 2 CPUs
>>>> [ 1.920299] smpboot: Max logical packages: 2
>>>> [ 1.921019] smpboot: Total of 2 processors activated (10774.03 BogoMIPS)
>>>
>>> After staring at it again, the change added in rebind_workers() is
>>> incorrect for a CPU getting back online after bootup, because the
>>> CPU affinity has been broken at offline time.
>>>
>>> But the warning in the latest report occurs at boot time, after going
>>> through steps like,
>>>
>>> kthread_create_on_node();
>>>
>>> kthread_bind_mask(worker->task, pool->attrs->cpumask);
>>>
>>> /* successful, attach the worker to the pool */
>>> worker_attach_to_pool(worker, pool, 0);
>>>
>>> /* start the newly created worker */
>>> wake_up_process(worker->task);
>>>
>>>
>>> without triggering the warning at kernel/kthread.c:507.
>>>
>>> Before finding an answer (wake_up_new_task()) to the question,
>>> who changed the allowed ptr? revert the change at online time,
>>> and as a compensation, clear POOL_DISASSOCIATED as early as we can.
>>>
>>>
>>> --- a/kernel/workqueue.c
>>> +++ b/kernel/workqueue.c
>>> @@ -1844,25 +1844,23 @@ static struct worker *alloc_worker(int n
>>> * cpu-[un]hotplugs.
>>> */
>>> static void worker_attach_to_pool(struct worker *worker,
>>> - struct worker_pool *pool)
>>> + struct worker_pool *pool, int set)
>>> {
>>> mutex_lock(&wq_pool_attach_mutex);
>>>
>>> /*
>>> - * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
>>> - * online CPUs. It'll be re-applied when any of the CPUs come up.
>>> - */
>>> - set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
>>> -
>>> - /*
>>> * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
>>> * stable across this function. See the comments above the flag
>>> * definition for details.
>>> */
>>> if (pool->flags & POOL_DISASSOCIATED)
>>> worker->flags |= WORKER_UNBOUND;
>>> - else
>>> + else {
>>> kthread_set_per_cpu(worker->task, true);
>>> + if (set)
>>> + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
>>> + pool->attrs->cpumask) < 0);
>>> + }
>>>
>>> list_add_tail(&worker->node, &pool->workers);
>>> worker->pool = pool;
>>> @@ -1943,7 +1941,7 @@ static struct worker *create_worker(stru
>>> kthread_bind_mask(worker->task, pool->attrs->cpumask);
>>>
>>> /* successful, attach the worker to the pool */
>>> - worker_attach_to_pool(worker, pool);
>>> + worker_attach_to_pool(worker, pool, 0);
>>>
>>> /* start the newly created worker */
>>> raw_spin_lock_irq(&pool->lock);
>>> @@ -2508,7 +2506,7 @@ repeat:
>>>
>>> raw_spin_unlock_irq(&wq_mayday_lock);
>>>
>>> - worker_attach_to_pool(rescuer, pool);
>>> + worker_attach_to_pool(rescuer, pool, 1);
>>>
>>> raw_spin_lock_irq(&pool->lock);
>>>
>>> @@ -4923,7 +4921,6 @@ static void unbind_workers(int cpu)
>>>
>>> for_each_pool_worker(worker, pool) {
>>> kthread_set_per_cpu(worker->task, false);
>>> - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
>>> }
>>>
>>> mutex_unlock(&wq_pool_attach_mutex);
>>> @@ -5954,6 +5951,7 @@ void __init workqueue_init_early(void)
>>> i = 0;
>>> for_each_cpu_worker_pool(pool, cpu) {
>>> BUG_ON(init_worker_pool(pool));
>>> + pool->flags &= ~POOL_DISASSOCIATED;
>>> pool->cpu = cpu;
>>> cpumask_copy(pool->attrs->cpumask, cpumask_of(cpu));
>>> pool->attrs->nice = std_nice[i++];
>>> --
>>>
>> I test the patch, the warning still appears in the kernel log.
>
> Thanks.
>>
>> [ 0.043584] masked ExtINT on CPU#1
>> [ 0.043584] smpboot: CPU 1 Converting physical 0 to logical die 1
>> [ 1.681867] ------------[ cut here ]------------
>> [ 1.681867] WARNING: CPU: 1 PID: 18 at kernel/workqueue.c:5015 workqueue_online_cpu+0x336/0x640
>
> This is a new one at boot time.
>
>> [ 1.681867] Modules linked in:
>> [ 1.681867] CPU: 1 PID: 18 Comm: cpuhp/1 Not tainted 5.11.0-rc3-00186-g178826956ca7 #2
>> [ 1.681867] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
>> [ 1.681867] EIP: workqueue_online_cpu+0x336/0x640
>> [ 1.681867] Code: 01 00 00 00 eb 89 8d b6 00 00 00 00 8b 5c 24 0c 89
>> d8 e8 3d 39 19 01 e9 1c fd ff ff 8d b4 26 00 00 00 00 90 ff 05 dc 20 04
>> 43 <0f> 0b e9 07 ff ff ff 8d 76 00 ff 05 2c 21 04 43 0f 0b e9 12 fe ff
>> [ 1.681867] EAX: 42f51168 EBX: 0000000c ECX: 00000000 EDX: 00000001
>> [ 1.681867] ESI: 00000000 EDI: 43c04720 EBP: de7f2564 ESP: 43d6bed0
>> [ 1.681867] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010002
>> [ 1.681867] CR0: 80050033 CR2: 00000000 CR3: 034e3000 CR4: 000406d0
>> [ 1.681867] Call Trace:
>> [ 1.681867] ? workqueue_prepare_cpu+0xa0/0xa0
>> [ 1.681867] ? cpuhp_invoke_callback+0x1ed/0x1340
>> [ 1.681867] ? cpuhp_thread_fun+0x28f/0x460
>> [ 1.681867] ? cpuhp_thread_fun+0x49/0x460
>> [ 1.681867] ? smpboot_thread_fn+0x446/0x620
>> [ 1.681867] ? kthread+0x1ba/0x1e0
>> [ 1.681867] ? __smpboot_create_thread+0x260/0x260
>> [ 1.681867] ? kzalloc+0x20/0x20
>> [ 1.681867] ? ret_from_fork+0x1c/0x28
>> [ 1.681867] ---[ end trace 3e853d8ad82e44ac ]---
>> [ 1.691939] kvm-guest: stealtime: cpu 1, msr 9e7e6ec0
>> [ 1.705909] smp: Brought up 1 node, 2 CPUs
>> [ 1.706605] smpboot: Max logical packages: 2
>>
>> [ 85.402803] smpboot: Booting Node 0 Processor 1 APIC 0x1
>> [ 85.442465] kvm-clock: cpu 1, msr 34f6021, secondary cpu clock
>> [ 85.442602] masked ExtINT on CPU#1
>> [ 85.541391] ------------[ cut here ]------------
>> [ 85.542250] WARNING: CPU: 1 PID: 18 at kernel/kthread.c:508 kthread_set_per_cpu+0x156/0x180
>
> This is a known one.
>
>> [ 85.543664] Modules linked in: rcutorture torture mousedev evbug
>> input_leds led_class psmouse pcspkr tiny_power_button button
>> [ 85.545530] CPU: 1 PID: 18 Comm: cpuhp/1 Tainted: G W
>> 5.11.0-rc3-00186-g178826956ca7 #2
>> [ 85.547006] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>> BIOS 1.12.0-1 04/01/2014
>> [ 85.548454] EIP: kthread_set_per_cpu+0x156/0x180
>> [ 85.549231] Code: 00 00 00 00 ff 05 68 4e 04 43 83 c4 08 5b 5e 5f c3
>> 8d 76 00 ff 05 34 50 04 43 0f 0b e9 f9 fe ff ff 8d 76 00 ff 05 2c 4e 04
>> 43 <0f> 0b eb 9d 8d b6 00 00 00 00 ff 05 40 4e 04 43 0f 0b e9 45 ff ff
>> [ 85.552236] EAX: 42f52ce0 EBX: 00000001 ECX: 00000000 EDX: 00000001
>> [ 85.556663] ESI: bfb70000 EDI: 45e61000 EBP: de7f2564 ESP: 43d6beb8
>> [ 85.559168] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010202
>> [ 85.561991] CR0: 80050033 CR2: 00000000 CR3: 034e3000 CR4: 000406d0
>> [ 85.563040] Call Trace:
>> [ 85.563463] ? workqueue_online_cpu+0x17f/0x640
>> [ 85.564222] ? rapl_cpu_online+0xb7/0x1a0
>> [ 85.564904] ? workqueue_prepare_cpu+0xa0/0xa0
>> [ 85.565643] ? cpuhp_invoke_callback+0x1ed/0x1340
>> [ 85.566424] ? cpuhp_thread_fun+0x28f/0x460
>> [ 85.567140] ? cpuhp_thread_fun+0x49/0x460
>> [ 85.567844] ? smpboot_thread_fn+0x446/0x620
>> [ 85.568569] ? kthread+0x1ba/0x1e0
>> [ 85.569162] ? __smpboot_create_thread+0x260/0x260
>> [ 85.569961] ? kzalloc+0x20/0x20
>> [ 85.570918] ? ret_from_fork+0x1c/0x28
>> [ 85.575418] ---[ end trace 3e853d8ad82e44ae ]---
>> [ 85.577919] kvm-guest: stealtime: cpu 1, msr 9e7e6ec0
>> [ 85.580973] ------------[ cut here ]------------
>> [ 85.581747] WARNING: CPU: 0 PID: 87 at kernel/workqueue.c:2190 process_one_work+0x92/0x9e0
>> [ 85.583058] Modules linked in: rcutorture torture mousedev evbug
>> input_leds led_class psmouse pcspkr tiny_power_button button
>> [ 85.584850] CPU: 0 PID: 87 Comm: kworker/1:2 Tainted: G W 5.11.0-rc3-00186-g178826956ca7 #2
>
> This is a big regression.
>
>> [ 85.586456] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>> BIOS 1.12.0-1 04/01/2014
>> [ 85.587753] Workqueue: 0x0 (rcu_gp)
>> [ 85.588347] EIP: process_one_work+0x92/0x9e0
>> [ 85.589018] Code: 37 64 a1 58 54 4c 43 39 45 24 74 2c 31 c9 ba 01 00
>> 00 00 c7 04 24 01 00 00 00 b8 d8 1c f5 42 e8 14 85 13 00 ff 05 a4 30 04
>> 43 <0f> 0b ba 01 00 00 00 eb 22 8d 74 26 00 90 c7 04 24 01 00 00 00 31
>> [ 85.595358] EAX: 42f51cd8 EBX: df4080f8 ECX: 00000000 EDX: 00000001
>> [ 85.596319] ESI: 43d94840 EDI: df4080f4 EBP: de7f23c0 ESP: 45505f08
>> [ 85.597291] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010002
>> [ 85.598410] CR0: 80050033 CR2: 372c2004 CR3: 7fa9f000 CR4: 000406d0
>> [ 85.599401] Call Trace:
>> [ 85.599804] ? process_one_work+0x20e/0x9e0
>> [ 85.600474] ? worker_thread+0x40d/0x6a0
>> [ 85.601096] ? kthread+0x1ba/0x1e0
>> [ 85.601635] ? create_worker+0x1e0/0x1e0
>> [ 85.602246] ? kzalloc+0x20/0x20
>> [ 85.602907] ? ret_from_fork+0x1c/0x28
>> [ 85.603512] ---[ end trace 3e853d8ad82e44af ]---
>> [ 85.699976] smpboot: CPU 1 is now offline
>> [ 85.771891] x86: Booting SMP configuration:
>> [ 85.772532] smpboot: Booting Node 0 Processor 1 APIC 0x1
>
> 1/ to fix the regression, roll back to the version without warning in
> process_one_work().
>
> 2/ to see if that version is utterly anything of a blind cat heading
> on a blind rat, quiesce the 508 warning for kworkers now.
>
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1844,25 +1844,23 @@ static struct worker *alloc_worker(int n
> * cpu-[un]hotplugs.
> */
> static void worker_attach_to_pool(struct worker *worker,
> - struct worker_pool *pool)
> + struct worker_pool *pool, int set)
> {
> mutex_lock(&wq_pool_attach_mutex);
>
> /*
> - * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
> - * online CPUs. It'll be re-applied when any of the CPUs come up.
> - */
> - set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
> -
> - /*
> * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
> * stable across this function. See the comments above the flag
> * definition for details.
> */
> if (pool->flags & POOL_DISASSOCIATED)
> worker->flags |= WORKER_UNBOUND;
> - else
> + else {
> kthread_set_per_cpu(worker->task, true);
> + if (set)
> + WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
> + pool->attrs->cpumask) < 0);
> + }
>
> list_add_tail(&worker->node, &pool->workers);
> worker->pool = pool;
> @@ -1943,7 +1941,7 @@ static struct worker *create_worker(stru
> kthread_bind_mask(worker->task, pool->attrs->cpumask);
>
> /* successful, attach the worker to the pool */
> - worker_attach_to_pool(worker, pool);
> + worker_attach_to_pool(worker, pool, 0);
>
> /* start the newly created worker */
> raw_spin_lock_irq(&pool->lock);
> @@ -2508,7 +2506,7 @@ repeat:
>
> raw_spin_unlock_irq(&wq_mayday_lock);
>
> - worker_attach_to_pool(rescuer, pool);
> + worker_attach_to_pool(rescuer, pool, 1);
>
> raw_spin_lock_irq(&pool->lock);
>
> @@ -4923,7 +4921,6 @@ static void unbind_workers(int cpu)
>
> for_each_pool_worker(worker, pool) {
> kthread_set_per_cpu(worker->task, false);
> - WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
> }
>
> mutex_unlock(&wq_pool_attach_mutex);
> @@ -4977,9 +4974,9 @@ static void rebind_workers(struct worker
> * from CPU_ONLINE, the following shouldn't fail.
> */
> for_each_pool_worker(worker, pool) {
> + kthread_set_per_cpu(worker->task, true);
> WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
> pool->attrs->cpumask) < 0);
> - kthread_set_per_cpu(worker->task, true);
> }
>
> raw_spin_lock_irq(&pool->lock);
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -505,7 +505,7 @@ void kthread_set_per_cpu(struct task_str
>
> if (set) {
> WARN_ON_ONCE(!(k->flags & PF_NO_SETAFFINITY));
> - WARN_ON_ONCE(k->nr_cpus_allowed != 1);
> + WARN_ON_ONCE(k->nr_cpus_allowed != 1 && !(k->flags & PF_WQ_WORKER));
> set_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
> } else {
> clear_bit(KTHREAD_IS_PER_CPU, &kthread->flags);
> --
>
I test the patch 4 times, no warning appears in the kernel log.
--
Zhengjun Xing