linux-kernel - Re: pciehp resume handler

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Date:	Wed, 01 Jul 2009 13:34:02 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
CC:	kristen.c.accardi@...el.com, linux-pci@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: pciehp resume handler - racy?

Alan Jenkins wrote:
> Hi,
> 
> I've been hacking on the PCI hotplug driver otherwise known as
> eeepc-laptop.  At one point I reliably triggered a race on resume.  In
> the hot-unplug case, it seemed that the resume handler would try to
> remove the PCI device at the same time as an acpi notification (run in a
> workqueue) tried to do the same thing.  The result was an OOPS.  My
> conclusion is that the PCI hotplug core does not protect against
> multiple simultaneous removals of the same device.

Though I don't know hotplug driver for eeepc-laptop at all, I guess
it doesn't use pci_hp_register(), which is for registering a hotplug
slot to pci hotplug core. The pci_hp_register() prevents a hot-plug
slot from being managed by multiple hotplug controller drivers at
the same time. Using pci_hp_register() would be one of the solution
for eeepc-laptop hotplug driver.

> 
> pciehp appears to have an analogous problem.  Assuming pciehp_force is
> set, the resume handler can hot-unplug the device.  The interrupt
> handler could try to hot-unplug the device at the same time.  Should the
> resume handler take the slot mutex to avoid this problem?
> 

Hot-plug operations for the same hotplug slot are serialized by
crit_sect mutex of struct controller in pciehp_enable_slot() and
pciehp_disable_slot(). So I don't think multiple hot-plug
operations for the same slot would be executed at the same time.

Thanks,
Kenji Kaneshige


> diff --faked-up a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
> --- a/drivers/pci/hotplug/pciehp_core.c
> +++ b/drivers/pci/hotplug/pciehp_core.c
> @@ -382,15 +382,18 @@ static int pciehp_resume (struct pcie_device *dev)
>  		/* reinitialize the chipset's event detection logic */
>  		pcie_enable_notification(ctrl);
>  
>  		t_slot = pciehp_find_slot(ctrl, ctrl->slot_device_offset);
> +		mutex_lock(&t_slot->lock);
>  
>  		/* Check if slot is occupied */
>  		t_slot->hpc_ops->get_adapter_status(t_slot, &status);
>  		if (status)
>  			pciehp_enable_slot(t_slot);
>  		else
>  			pciehp_disable_slot(t_slot);
> +
> +		mutex_unlock(&t_slot->lock);
>  	}
>  	return 0;
>  }
>  #endif /* PM */
> 
> 
> Regards
> Alan
> 
> --
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> 
> 


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