On Thu, Jun 29, 2023 at 9:33 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > 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. Um, yes, you are right as usual. It was clear to me from the code that NOWAIT is not used with swap under VMA_LOCK, that's why I didn't consider this check earlier. Yeah, patch 3 seems like a more appropriate place for it. I'll move it and post a new patchset later today or tomorrow morning with your Acks. Thanks, Suren. > > Thanks, > > -- > Peter Xu >
