On Mon, May 25, 2020 at 09:26:07AM -0300, Jason Gunthorpe wrote: > On Sat, May 23, 2020 at 07:52:57PM -0400, Peter Xu wrote: > > > For what I understand now, IMHO we should still need all those handlings of > > FAULT_FLAG_RETRY_NOWAIT like in the initial version. E.g., IIUC KVM gup will > > try with FOLL_NOWAIT when async is allowed, before the complete slow path. I'm > > not sure what would be the side effect of that if fault() blocked it. E.g., > > the caller could be in an atomic context. > > AFAICT FAULT_FLAG_RETRY_NOWAIT only impacts what happens when > VM_FAULT_RETRY is returned, which this doesn't do? Yes, that's why I think we should still properly return VM_FAULT_RETRY if needed.. because IMHO it is still possible that the caller calls with FAULT_FLAG_RETRY_NOWAIT. My understanding is that FAULT_FLAG_RETRY_NOWAIT majorly means: - We cannot release the mmap_sem, and, - We cannot sleep But we're allowed to return VM_FAULT_RETRY if any of the above is necessary. Thanks, -- Peter Xu
