On 30/10/2022 18:23, Alan Stern wrote:
It looks like the xillybus driver already has a private mutex that would have been very well suited for this task: unit_mutex defined in xillybus_class.c.
Indeed so. The problem is that unit_mutex is global to xillybus_class.c, and I need the mutex to be released in xillyusb.c: The kref counter, which needs to be incremented with a mutex held, is inside a structure that only the XillyUSB driver knows about, so xillybus_class can't do that. Which is why xillybus_find_inode() passed a pointer to unit_mutex to its caller in the v1 version of this patch. But that turned out to be too odd.
Of course, there's nothing wrong with using a new mutex instead -- just make sure there aren't any ABBA locking order problems.
The kref_mutex is always taken with no other (Xillybus-related) mutex taken. So the locking order is assured.
But thanks for the reminder. Never hurts checking again. Regards, Eli
