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

[Greg KH <gregkh@linuxfoundation.org>]

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.

confused,

greg k-h