[PATCH RFC 20/24] userfaultfd: wp: don't wake up when doing write protect

Peter Xu
2019-01-21T08:00:13Z

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.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
fs/userfaultfd.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 455b87c0596f..e54ab6076e13 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;

user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;

@@ -1786,17 +1787,19 @@ 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);
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