On Thu, Jan 14, 2021 at 04:42:48PM +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
> > 
> > 
> > in testcase: rcutorture
> > version: 
> > with following parameters:
> > 
> > 	runtime: 300s
> > 	test: cpuhotplug
> > 	torture_type: srcud
> > 
> > test-description: rcutorture is rcutorture kernel module load/unload test.
> > test-url: https://www.kernel.org/doc/Documentation/RCU/torture.txt
> > 
> > 
> > on test machine: qemu-system-i386 -enable-kvm -cpu SandyBridge -smp 2 -m 8G
> > 
> > caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> > 
> > 
> > +--------------------------------------------------+------------+------------+
> > |                                                  | 6211b34f6e | d5bff968ea |
> > +--------------------------------------------------+------------+------------+
> > | boot_successes                                   | 4          | 0          |
> > | boot_failures                                    | 0          | 12         |
> > | WARNING:at_kernel/workqueue.c:#process_one_work  | 0          | 12         |
> > | EIP:process_one_work                             | 0          | 12         |
> > | WARNING:at_kernel/kthread.c:#kthread_set_per_cpu | 0          | 4          |
> > | EIP:kthread_set_per_cpu                          | 0          | 4          |
> > +--------------------------------------------------+------------+------------+
> > 
> > 
> > If you fix the issue, kindly add following tag
> > Reported-by: kernel test robot <oliver.sang@intel.com>
> > 
> > 
> > [   73.794288] WARNING: CPU: 0 PID: 22 at kernel/workqueue.c:2192 process_one_work (kbuild/src/consumer/kernel/workqueue.c:2192) 
> > [   73.795012] Modules linked in: rcutorture torture mousedev evbug input_leds led_class psmouse pcspkr tiny_power_button button
> > [   73.795949] CPU: 0 PID: 22 Comm: kworker/1:0 Not tainted 5.11.0-rc3-gd5bff968ea9c #2
> > [   73.796592] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
> > [   73.797280] Workqueue:  0x0 (rcu_gp)
> > [   73.797592] EIP: process_one_work (kbuild/src/consumer/kernel/workqueue.c:2192) 
> 
> 
> Can you run the reproducer with the changes to WQ cut?

hi, by applying below patch, the issue still happened. detail dmesg is attached.

[ 2.505530] TCP: Hash tables configured (established 32768 bind 32768)
[ 2.506668] -----------[ cut here ]-----------
[ 2.508080] WARNING: CPU: 0 PID: 23 at kernel/workqueue.c:2190 process_one_work+0x92/0x9e0
[ 2.509963] Modules linked in:
[ 2.510692] CPU: 0 PID: 23 Comm: kworker/1:0H Not tainted 5.11.0-rc3-00186-ge7792535d216 #2
[ 2.512608] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
[ 2.514499] EIP: process_one_work+0x92/0x9e0
[ 2.515468] 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
[ 2.516539] EAX: 42f51d08 EBX: 00000000 ECX: 00000000 EDX: 00000001
[ 2.516539] ESI: 43c04780 EDI: de7eb3ec EBP: de7f25e0 ESP: 43d83f08
[ 2.516539] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010002
[ 2.516539] CR0: 80050033 CR2: 00000000 CR3: 034e3000 CR4: 000406d0
[ 2.516539] Call Trace:
[ 2.516539] ? rcuwait_wake_up+0x53/0x80
[ 2.516539] ? rcuwait_wake_up+0x5/0x80
[ 2.516539] ? worker_thread+0x2dd/0x6a0
[ 2.516539] ? kthread+0x1ba/0x1e0
[ 2.516539] ? create_worker+0x1e0/0x1e0
[ 2.516539] ? kzalloc+0x20/0x20
[ 2.516539] ? ret_from_fork+0x1c/0x28
[ 2.516539] --[ end trace 71c162214dd31179 ]--
[ 2.534063] UDP hash table entries: 2048 (order: 5, 196608 bytes, linear)
[ 2.535774] UDP-Lite hash table entries: 2048 (order: 5, 196608 bytes, linear)
[ 2.537661] NET: Registered protocol family 1

> 
> It seems special to make kworker pcpu because they are going not to
> help either hotplug or stop. If it quiesces the warning then we have
> a fresh start for breaking CPU affinity.
> 
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1861,8 +1861,6 @@ static void worker_attach_to_pool(struct
>  	 */
>  	if (pool->flags & POOL_DISASSOCIATED)
>  		worker->flags |= WORKER_UNBOUND;
> -	else
> -		kthread_set_per_cpu(worker->task, true);
>  
>  	list_add_tail(&worker->node, &pool->workers);
>  	worker->pool = pool;
> @@ -4922,7 +4920,6 @@ static void unbind_workers(int cpu)
>  		raw_spin_unlock_irq(&pool->lock);
>  
>  		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);
>  		}
>  
> @@ -4979,7 +4976,6 @@ static void rebind_workers(struct worker
>  	for_each_pool_worker(worker, pool) {
>  		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);