On Wed, Nov 18, 2020 at 09:45:40AM +0800, Boqun Feng wrote: > Hi Matthew, > > On Mon, Nov 16, 2020 at 03:37:29PM +0000, Matthew Wilcox wrote: > [...] > > > > It's not just about lockdep for semaphores. Mutexes will spin if the > > current owner is still running, so to convert an interrupt-released > > semaphore to a mutex, we need a way to mark the mutex as being released > > Could you provide an example for the conversion from interrupt-released > semaphore to a mutex? I'd like to see if we can improve lockdep to help > on that case.
How about adb_probe_mutex in drivers/macintosh/adb.c. Most of the acquires/releases are within the same task. But adb_reset_bus() calls down(&adb_probe_mutex), then schedules adb_reset_work() which runs adb_probe_task() which calls up(&adb_probe_mutex). Ideally adb_probe_mutex would become a mutex instead of the semaphore it currently is. adb_reset_bus() would pass ownership of the mutex to kadbprobe since it's the one which must run in order to release the mutex.
