On Tue, Oct 25, 2022 at 11:21:49AM -0700, Axel Rasmussen wrote:
> This was an overlooked edge case when minor faults were added. In
> general, minor faults have the same rough edge here as missing faults:
> if we unregister while there are waiting threads, they will just remain
> waiting forever, as there is no way for userspace to wake them after
> unregistration. To work around this, userspace needs to carefully wake
> everything before unregistering.
>
> So, wake for minor faults just like we already do for missing faults as
> part of the unregistration process.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 7677f7fd8be7 ("userfaultfd: add minor fault registration mode")
> Reported-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
> Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
> ---
> fs/userfaultfd.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 07c81ab3fd4d..7daee4b9481c 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1606,7 +1606,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> start = vma->vm_start;
> vma_end = min(end, vma->vm_end);
>
> - if (userfaultfd_missing(vma)) {
> + if (userfaultfd_missing(vma) || userfaultfd_minor(vma)) {
> /*
> * Wake any concurrent pending userfault while
> * we unregister, so they will not hang
> --
> 2.38.0.135.g90850a2211-goog
Thanks, Axel. Is wr-protect mode also prone to this? Would a test case
help too?
--
Peter Xu
