Re: [PATCH v2 4/4] PCI/AER: fix a small race condition window when rmmod aer_inject

[Huang Ying <ying.huang@intel.com>]

On Wed, 2012-09-12 at 20:33 +0800, Yijing Wang wrote:
> Fix a small race condition window between pci_bus_ops_pop() and
> pci_bus_set_ops() functions.
> 
> Signed-off-by: Yijing Wang <wangyijing@huawei.com>
> Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
> ---
>  drivers/pci/pcie/aer/aer_inject.c |    8 ++------
>  1 files changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/pcie/aer/aer_inject.c b/drivers/pci/pcie/aer/aer_inject.c
> index bd043db..69c2d77 100644
> --- a/drivers/pci/pcie/aer/aer_inject.c
> +++ b/drivers/pci/pcie/aer/aer_inject.c
> @@ -141,12 +141,11 @@ static struct pci_ops *__find_pci_bus_ops(struct pci_bus *bus)
>  	return NULL;
>  }
>  
> +/* inject_lock must be held before calling */
>  static struct pci_bus_ops *pci_bus_ops_pop(void)
>  {
> -	unsigned long flags;
>  	struct pci_bus_ops *bus_ops = NULL;
>  
> -	spin_lock_irqsave(&inject_lock, flags);
>  	if (list_empty(&pci_bus_ops_list))
>  		bus_ops = NULL;
>  	else {
> @@ -154,7 +153,6 @@ static struct pci_bus_ops *pci_bus_ops_pop(void)
>  		list_del(lh);
>  		bus_ops = list_entry(lh, struct pci_bus_ops, list);
>  	}
> -	spin_unlock_irqrestore(&inject_lock, flags);
>  	return bus_ops;
>  }
>  
> @@ -610,14 +608,12 @@ static void __exit aer_inject_exit(void)
>  	bus_unregister_notifier(&pci_bus_type, &aerinj_hp_notifier);
>  	misc_deregister(&aer_inject_device);
>  
> +	spin_lock_irqsave(&inject_lock, flags);
>  	while ((bus_ops = pci_bus_ops_pop())) {
>  		pci_bus_set_ops(bus_ops->bus, bus_ops->ops);
>  		kfree(bus_ops);
>  	}
>  	
> -	clean_untracked_pci_aer_ops();
> -
> -	spin_lock_irqsave(&inject_lock, flags);
>  	list_for_each_entry_safe(err, err_next, &einjected, list) {
>  		list_del(&err->list);
>  		kfree(err);

This may trigger a AB BA dead lock.  In aer_inject_exit, the lock
sequence is:

inject_lock -> pci_lock

In pci config read/write path, the lock sequence is:

pci_lock -> inject_lock

With lockdep enabled, you may found warning on that.

Best Regards,
Huang YIng