Subject: Re: [PATCH net] virtio-net: correctly handle cpu hotplug notifier during resuming

From: Wanlong Gao <[email-masked]>
Date: Tue, 29 Oct 2013 16:42:27 +0800

On 10/29/2013 03:11 PM, Jason Wang wrote:
> commit 3ab098df35f8b98b6553edc2e40234af512ba877 (virtio-net: don't respond to
> cpu hotplug notifier if we're not ready) tries to bypass the cpu hotplug
> notifier by checking the config_enable and does nothing is it was false. So it
> need to try to hold the config_lock mutex which may happen in atomic
> environment which leads the following warnings:
> 
> [  622.944441] CPU0 attaching NULL sched-domain.
> [  622.944446] CPU1 attaching NULL sched-domain.
> [  622.944485] CPU0 attaching NULL sched-domain.
> [  622.950795] BUG: sleeping function called from invalid context at kernel/mutex.c:616
> [  622.950796] in_atomic(): 1, irqs_disabled(): 1, pid: 10, name: migration/1
> [  622.950796] no locks held by migration/1/10.
> [  622.950798] CPU: 1 PID: 10 Comm: migration/1 Not tainted 3.12.0-rc5-wl-01249-gb91e82d #317
> [  622.950799] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [  622.950802]  0000000000000000 ffff88001d42dba0 ffffffff81a32f22 ffff88001bfb9c70
> [  622.950803]  ffff88001d42dbb0 ffffffff810edb02 ffff88001d42dc38 ffffffff81a396ed
> [  622.950805]  0000000000000046 ffff88001d42dbe8 ffffffff810e861d 0000000000000000
> [  622.950805] Call Trace:
> [  622.950810]  [<ffffffff81a32f22>] dump_stack+0x54/0x74
> [  622.950815]  [<ffffffff810edb02>] __might_sleep+0x112/0x114
> [  622.950817]  [<ffffffff81a396ed>] mutex_lock_nested+0x3c/0x3c6
> [  622.950818]  [<ffffffff810e861d>] ? up+0x39/0x3e
> [  622.950821]  [<ffffffff8153ea7c>] ? acpi_os_signal_semaphore+0x21/0x2d
> [  622.950824]  [<ffffffff81565ed1>] ? acpi_ut_release_mutex+0x5e/0x62
> [  622.950828]  [<ffffffff816d04ec>] virtnet_cpu_callback+0x33/0x87
> [  622.950830]  [<ffffffff81a42576>] notifier_call_chain+0x3c/0x5e
> [  622.950832]  [<ffffffff810e86a8>] __raw_notifier_call_chain+0xe/0x10
> [  622.950835]  [<ffffffff810c5556>] __cpu_notify+0x20/0x37
> [  622.950836]  [<ffffffff810c5580>] cpu_notify+0x13/0x15
> [  622.950838]  [<ffffffff81a237cd>] take_cpu_down+0x27/0x3a
> [  622.950841]  [<ffffffff81136289>] stop_machine_cpu_stop+0x93/0xf1
> [  622.950842]  [<ffffffff81136167>] cpu_stopper_thread+0xa0/0x12f
> [  622.950844]  [<ffffffff811361f6>] ? cpu_stopper_thread+0x12f/0x12f
> [  622.950847]  [<ffffffff81119710>] ? lock_release_holdtime.part.7+0xa3/0xa8
> [  622.950848]  [<ffffffff81135e4b>] ? cpu_stop_should_run+0x3f/0x47
> [  622.950850]  [<ffffffff810ea9b0>] smpboot_thread_fn+0x1c5/0x1e3
> [  622.950852]  [<ffffffff810ea7eb>] ? lg_global_unlock+0x67/0x67
> [  622.950854]  [<ffffffff810e36b7>] kthread+0xd8/0xe0
> [  622.950857]  [<ffffffff81a3bfad>] ? wait_for_common+0x12f/0x164
> [  622.950859]  [<ffffffff810e35df>] ? kthread_create_on_node+0x124/0x124
> [  622.950861]  [<ffffffff81a45ffc>] ret_from_fork+0x7c/0xb0
> [  622.950862]  [<ffffffff810e35df>] ? kthread_create_on_node+0x124/0x124
> [  622.950876] smpboot: CPU 1 is now offline
> [  623.194556] SMP alternatives: lockdep: fixing up alternatives
> [  623.194559] smpboot: Booting Node 0 Processor 1 APIC 0x1
> ...
> 
> A correct fix is to unregister the hotcpu notifier during restore and register a
> new one in resume.
> 
> Reported-by: Fengguang Wu <[email-masked]>
> Tested-by: Fengguang Wu <[email-masked]>
> Cc: Wanlong Gao <[email-masked]>
> Cc: Rusty Russell <[email-masked]>
> Cc: Michael S. Tsirkin <[email-masked]>
> Signed-off-by: Jason Wang <[email-masked]>

Thank you for your fix.

Reviewed-by: Wanlong Gao <[email-masked]>

> ---
> This patch is needed for 3.8 and above.
> ---
>  drivers/net/virtio_net.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9fbdfcd..bbc9cb8 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1118,11 +1118,6 @@ static int virtnet_cpu_callback(struct notifier_block *nfb,
>  {
>  	struct virtnet_info *vi = container_of(nfb, struct virtnet_info, nb);
>  
> -	mutex_lock(&vi->config_lock);
> -
> -	if (!vi->config_enable)
> -		goto done;
> -
>  	switch(action & ~CPU_TASKS_FROZEN) {
>  	case CPU_ONLINE:
>  	case CPU_DOWN_FAILED:
> @@ -1136,8 +1131,6 @@ static int virtnet_cpu_callback(struct notifier_block *nfb,
>  		break;
>  	}
>  
> -done:
> -	mutex_unlock(&vi->config_lock);
>  	return NOTIFY_OK;
>  }
>  
> @@ -1699,6 +1692,8 @@ static int virtnet_freeze(struct virtio_device *vdev)
>  	struct virtnet_info *vi = vdev->priv;
>  	int i;
>  
> +	unregister_hotcpu_notifier(&vi->nb);
> +
>  	/* Prevent config work handler from accessing the device */
>  	mutex_lock(&vi->config_lock);
>  	vi->config_enable = false;
> @@ -1747,6 +1742,10 @@ static int virtnet_restore(struct virtio_device *vdev)
>  	virtnet_set_queues(vi, vi->curr_queue_pairs);
>  	rtnl_unlock();
>  
> +	err = register_hotcpu_notifier(&vi->nb);
> +	if (err)
> +		return err;
> +
>  	return 0;
>  }
>  #endif
>