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@vger.kernel.org Fixes: 7677f7fd8be7 ("userfaultfd: add minor fault registration mode") Reported-by: Lokesh Gidra lokeshgidra@google.com Signed-off-by: Axel Rasmussen axelrasmussen@google.com
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?