linux-kernel - Re: [PATCH] USB: additional regression fix for device removal

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Date:	Thu, 07 Jul 2011 10:36:05 +0200
From:	Éric Piel <E.A.B.Piel@...elft.nl>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Greg KH <gregkh@...e.de>,
	Arkadiusz Miskiewicz <a.miskiewicz@...il.com>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH] USB: additional regression fix for device removal

Op 06-07-11 23:03, Alan Stern schreef:
> Commit e534c5b831c8b8e9f5edee5c8a37753c808b80dc (USB: fix regression
> occurring during device removal) didn't go far enough.  It failed to
> take into account that when a driver claims multiple interfaces, it may
> release them all at the same time.  As a result, some interfaces can
> get released before they are unregistered, and we deadlock trying to
> acquire the bandwidth_mutex that we already own.
>
> This patch (asl478) handles this case by setting the "unregistering"
> flag on all the interfaces before removing any of them.
>
> Signed-off-by: Alan Stern<stern@...land.harvard.edu>
> CC:<stable@...nel.org>

Great, it works here :-)
Tested-by: Éric Piel <eric.piel@...mplin-utc.net>

Thanks,
Éric
>
> ---
>
> This should take care of Eric's problem as well as Arkadiusz, since
> they seemed to be hitting the same thing (cdc_ether claiming multiple
> interfaces and hanging while releasing them).
>
> Still, we need to rewrite this stuff.  A possible race remains, because
> a driver may try to change an altsetting at the same time as the device
> is removed.  Either the driver's disconnect routine would hang waiting
> for the altsetting change (which is waiting to acquire the
> bandwidth_mutex) or else the altsetting change would go through after
> the driver was unbound from the device.  Neither alternative is good.
>
> Alan Stern
>
>
>
>   drivers/usb/core/message.c |    9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
>
> Index: usb-3.0/drivers/usb/core/message.c
> ===================================================================
> --- usb-3.0.orig/drivers/usb/core/message.c
> +++ usb-3.0/drivers/usb/core/message.c
> @@ -1147,6 +1147,14 @@ void usb_disable_device(struct usb_devic
>   	 * any drivers bound to them (a key side effect)
>   	 */
>   	if (dev->actconfig) {
> +		/*
> +		 * FIXME: In order to avoid self-deadlock involving the
> +		 * bandwidth_mutex, we have to mark all the interfaces
> +		 * before unregistering any of them.
> +		 */
> +		for (i = 0; i<  dev->actconfig->desc.bNumInterfaces; i++)
> +			dev->actconfig->interface[i]->unregistering = 1;
> +
>   		for (i = 0; i<  dev->actconfig->desc.bNumInterfaces; i++) {
>   			struct usb_interface	*interface;
>
> @@ -1156,7 +1164,6 @@ void usb_disable_device(struct usb_devic
>   				continue;
>   			dev_dbg(&dev->dev, "unregistering interface %s\n",
>   				dev_name(&interface->dev));
> -			interface->unregistering = 1;
>   			remove_intf_ep_devs(interface);
>   			device_del(&interface->dev);
>   		}
>

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