Re: usb storage lockdep report.

[Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>]

On Wed, 14 Mar 2012, Alan Stern wrote:

> On Thu, 15 Mar 2012, Ming Lei wrote:
> 
> > On Thu, Mar 15, 2012 at 12:04 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> > 
> > > Is there any way to reproduce this?
> > >
> > > It seems to be saying that usb_stor_pre_reset() was called twice
> > > without usb_stor_post_reset() being called in between, because the
> > > post_reset routine is where the lock gets released. �I don't know of
> > > any way that could happen.
> > 
> > Looks it is a device with multiple usb mass interfaces, care to
> > post the 'lsusb -v' of the device?
> > 
> > If so, the following patch should remove the warning.
> > 
> > diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
> > index c18538e..1c209a0 100644
> > --- a/drivers/usb/storage/usb.c
> > +++ b/drivers/usb/storage/usb.c
> > @@ -194,11 +194,13 @@ EXPORT_SYMBOL_GPL(usb_stor_reset_resume);
> >  int usb_stor_pre_reset(struct usb_interface *iface)
> >  {
> >  	struct us_data *us = usb_get_intfdata(iface);
> > +	int if_num = (int)(iface -
> > +			us->pusb_dev->actconfig->interface[0]);
> > 
> >  	US_DEBUGP("%s\n", __func__);
> > 
> >  	/* Make sure no command runs during the reset */
> > -	mutex_lock(&us->dev_mutex);
> > +	mutex_lock_nested(&us->dev_mutex, if_num);
> >  	return 0;
> >  }
> >  EXPORT_SYMBOL_GPL(usb_stor_pre_reset);
> 
> No, it won't fix the problem.  It will work once, say when the driver
> for interface 0 does a reset and calls the routine for interface 1.  
> But then what will happen when the driver for interface 1 does a reset
> and calls the routine for interface 0?

I take this back.  It doesn't matter which driver thread does the
reset, because the usb_reset_device() routine always calls the
pre_reset methods in the same order.  So yes, this patch should indeed
fix the problem.

On the other hand, that order is given by the entries in the
us->pusb_dev->actconfig array, not by the interface numbers.  
Therefore this original version of the patch should be used instead of
the revised version.

Alan Stern

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