[PATCH v3 23/28] 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 <r...@linux.vnet.ibm.com>
Signed-off-by: Peter Xu <pet...@redhat.com>
---
 fs/userfaultfd.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 81962d62520c..f1f61a0278c2 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1771,6 +1771,7 @@ 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;
@@ -1789,18 +1790,20 @@ 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);
-- 
2.17.1