On Wed, Feb 23, 2022 at 10:09:01AM -0400, Jason Gunthorpe wrote: > On Wed, Feb 23, 2022 at 03:06:35PM +0100, Greg Kroah-Hartman wrote: > > On Wed, Feb 23, 2022 at 09:46:27AM -0400, Jason Gunthorpe wrote: > > > On Wed, Feb 23, 2022 at 01:04:00PM +0000, Robin Murphy wrote: > > > > > > > 1 - tmp->driver is non-NULL because tmp is already bound. > > > > 1.a - If tmp->driver->driver_managed_dma == 0, the group must currently be > > > > DMA-API-owned as a whole. Regardless of what driver dev has unbound from, > > > > its removal does not release someone else's DMA API (co-)ownership. > > > > > > This is an uncommon locking pattern, but it does work. It relies on > > > the mutex being an effective synchronization barrier for an unlocked > > > store: > > > > > > WRITE_ONCE(dev->driver, NULL) > > > > Only the driver core should be messing with the dev->driver pointer as > > when it does so, it already has the proper locks held. Do I need to > > move that to a "private" location so that nothing outside of the driver > > core can mess with it? > > It would be nice, I've seen a abuse and mislocking of it in drivers Though to be clear, what Robin is describing is still keeping the dev->driver stores in dd.c, just reading it in a lockless way from other modules. Jason
