[PATCH v5 21/25] userfaultfd: wp: don't wake up when doing write protect

[Peter Xu]

It does not make sense to try to wake up any waiting thread when we're
write-protecting a memory region.  Only wake up when resolving a write
protected page fault.

Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
 fs/userfaultfd.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 3cf19aeaa0e0..498971fa9163 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1782,6 +1782,7 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
 	struct uffdio_writeprotect uffdio_wp;
 	struct uffdio_writeprotect __user *user_uffdio_wp;
 	struct userfaultfd_wake_range range;
+	bool mode_wp, mode_dontwake;
 
 	if (READ_ONCE(ctx->mmap_changing))
 		return -EAGAIN;
@@ -1800,18 +1801,20 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
 	if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
 			       UFFDIO_WRITEPROTECT_MODE_WP))
 		return -EINVAL;
-	if ((uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP) &&
-	     (uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE))
+
+	mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
+	mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
+
+	if (mode_wp && mode_dontwake)
 		return -EINVAL;
 
 	ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
-				  uffdio_wp.range.len, uffdio_wp.mode &
-				  UFFDIO_WRITEPROTECT_MODE_WP,
+				  uffdio_wp.range.len, mode_wp,
 				  &ctx->mmap_changing);
 	if (ret)
 		return ret;
 
-	if (!(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) {
+	if (!mode_wp && !mode_dontwake) {
 		range.start = uffdio_wp.range.start;
 		range.len = uffdio_wp.range.len;
 		wake_userfault(ctx, &range);
-- 
2.21.0