Hi Dave, On Tue, Jun 23, 2015 at 12:00:19PM -0700, Dave Hansen wrote: > Down in userfaultfd_wake_function(), it looks like you intended for a > len=0 to mean "wake all". But the validate_range() that we do from > userspace has a !len check in it, which keeps us from passing a len=0 in > from userspace. > Was that "wake all" for some internal use, or is the check too strict? It's for internal use or userfaultfd_release that has to wake them all (after setting ctx->released) if the uffd is closed. It avoids to enlarge the structure by depending on the invariant that userland cannot pass len=0. If we'd accept len=0 from userland as valid, I'd be safer if it does nothing like in madvise, I doubt we want to expose this non standard kernel internal behavior to userland. > I was trying to use the wake ioctl after an madvise() (as opposed to > filling things in using a userfd copy). madvise will return 0 if len=0, mremap would return -EINVAL if new_len is zero, mmap also returns -EINVAL if len is 0, not all MM syscalls are as permissive as madvise. Can't you pass the same len you pass to madvise to UFFDIO_WAKE (or just skip the call if the madvise len is zero)? Thanks, Andrea -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>