Re: [PATCH 2/2] USB: core: Fix deadlock in port "disable" sysfs attribute

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Mar 26, 2024 at 10:22:32AM +0100, Greg KH wrote:
> On Fri, Mar 15, 2024 at 01:06:33PM -0400, Alan Stern wrote:
> > The show and store callback routines for the "disable" sysfs attribute
> > file in port.c acquire the device lock for the port's parent hub
> > device.  This can cause problems if another process has locked the hub
> > to remove it or change its configuration:
> > 
> > 	Removing the hub or changing its configuration requires the
> > 	hub interface to be removed, which requires the port device
> > 	to be removed, and device_del() waits until all outstanding
> > 	sysfs attribute callbacks for the ports have returned.  The
> > 	lock can't be released until then.
> > 
> > 	But the disable_show() or disable_store() routine can't return
> > 	until after it has acquired the lock.
> > 
> > The resulting deadlock can be avoided by calling
> > sysfs_break_active_protection().  This will cause the sysfs core not
> > to wait for the attribute's callback routine to return, allowing the
> > removal to proceed.  The disadvantage is that after making this call,
> > there is no guarantee that the hub structure won't be deallocated at
> > any moment.  To prevent this, we have to acquire a reference to it
> > first by calling hub_get().
> > 
> > Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> > Cc: <stable@vger.kernel.org>	# Needs the previous patch in this series
> 
> What "previous patch"?  I don't see this as a series even on
> lore.kernel.org.

Ah, found it, you sent it only to me for some reason, and not the lists.

thanks,

greg k-h