On Wed, Jun 28, 2023 at 05:19:31PM -0700, Suren Baghdasaryan wrote: > On Wed, Jun 28, 2023 at 10:32 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > > > On Wed, Jun 28, 2023 at 10:25:29AM -0700, Suren Baghdasaryan wrote: > > > Enable handle_userfault to operate under VMA lock by releasing VMA lock > > > instead of mmap_lock and retrying. Note that FAULT_FLAG_RETRY_NOWAIT > > > should never be used when handling faults under per-VMA lock protection > > > because that would break the assumption that lock is dropped on retry. > > > > > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > > > > Maybe the sanitize_fault_flags() changes suite more in patch 3, but not a > > big deal I guess. > > IIUC FAULT_FLAG_RETRY_NOWAIT comes into play in this patchset only in > the context of uffds, therefore that check seems to be needed when we > enable per-VMA lock uffd support, which is this patch. Does that make > sense? I don't see why uffd is special in this regard, as e.g. swap also checks NOWAIT when folio_lock_or_retry() so I assume it's also used there. IMHO the "NOWAIT should never apply with VMA_LOCK so far" assumption starts from patch 3 where it conditionally releases the vma lock when !(RETRY|COMPLETE); that is the real place where it can start to go wrong if anyone breaks the assumption. Thanks, -- Peter Xu
