On Tue, Dec 07, 2021 at 05:25:04AM -0800, Christoph Hellwig wrote: > On Tue, Dec 07, 2021 at 09:16:27AM -0400, Jason Gunthorpe wrote: > > Yes, the suggestion was to put everything that 'if' inside a function > > and then of course a matching undo function. > > Can't we simplify things even more? Do away with the DMA API owner > entirely, and instead in iommu_group_set_dma_owner iterate over all > devices in a group and check that they all have the no_dma_api flag > set (plus a similar check on group join). With that most of the > boilerplate code goes away entirely in favor of a little more work at > iommu_group_set_dma_owner time. Robin suggested something like this already. The locking doesn't work out, we can't nest device_lock()'s safely without ABBA deadlocks, and can't touch the dev->driver without the device_lock. Jason
