From: Alan Stern stern@rowland.harvard.edu
commit 65dadb2beeb7360232b09ebc4585b54475dfee06 upstream.
Avichal Rakesh reported a kernel panic that occurred when the UVC gadget driver was removed from a gadget's configuration. The panic involves a somewhat complicated interaction between the kernel driver and a userspace component (as described in the Link tag below), but the analysis did make one thing clear: The Gadget core should accomodate gadget drivers calling usb_gadget_deactivate() as part of their unbind procedure.
Currently this doesn't work. gadget_unbind_driver() calls driver->unbind() while holding the udc->connect_lock mutex, and usb_gadget_deactivate() attempts to acquire that mutex, which will result in a deadlock.
The simple fix is for gadget_unbind_driver() to release the mutex when invoking the ->unbind() callback. There is no particular reason for it to be holding the mutex at that time, and the mutex isn't held while the ->bind() callback is invoked. So we'll drop the mutex before performing the unbind callback and reacquire it afterward.
We'll also add a couple of comments to usb_gadget_activate() and usb_gadget_deactivate(). Because they run in process context they must not be called from a gadget driver's ->disconnect() callback, which (according to the kerneldoc for struct usb_gadget_driver in include/linux/usb/gadget.h) may run in interrupt context. This may help prevent similar bugs from arising in the future.
Reported-and-tested-by: Avichal Rakesh arakesh@google.com Signed-off-by: Alan Stern stern@rowland.harvard.edu Fixes: 286d9975a838 ("usb: gadget: udc: core: Prevent soft_connect_store() race") Link: https://lore.kernel.org/linux-usb/4d7aa3f4-22d9-9f5a-3d70-1bd7148ff4ba@googl... Cc: Badhri Jagan Sridharan badhri@google.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/48b2f1f1-0639-46bf-bbfc-98cb05a24914@rowland.harva... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/gadget/udc/core.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c index cd58f2a4e7f3..7d49d8a0b00c 100644 --- a/drivers/usb/gadget/udc/core.c +++ b/drivers/usb/gadget/udc/core.c @@ -822,6 +822,9 @@ EXPORT_SYMBOL_GPL(usb_gadget_disconnect); * usb_gadget_activate() is called. For example, user mode components may * need to be activated before the system can talk to hosts. * + * This routine may sleep; it must not be called in interrupt context + * (such as from within a gadget driver's disconnect() callback). + * * Returns zero on success, else negative errno. */ int usb_gadget_deactivate(struct usb_gadget *gadget) @@ -860,6 +863,8 @@ EXPORT_SYMBOL_GPL(usb_gadget_deactivate); * This routine activates gadget which was previously deactivated with * usb_gadget_deactivate() call. It calls usb_gadget_connect() if needed. * + * This routine may sleep; it must not be called in interrupt context. + * * Returns zero on success, else negative errno. */ int usb_gadget_activate(struct usb_gadget *gadget) @@ -1638,7 +1643,11 @@ static void gadget_unbind_driver(struct device *dev) usb_gadget_disable_async_callbacks(udc); if (gadget->irq) synchronize_irq(gadget->irq); + mutex_unlock(&udc->connect_lock); + udc->driver->unbind(gadget); + + mutex_lock(&udc->connect_lock); usb_gadget_udc_stop_locked(udc); mutex_unlock(&udc->connect_lock);