userfaultfd: wp: don't wake up when doing write protect

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20200220163112.11409-16-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 59e9e39..6e878d2 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1812,6 +1812,7 @@ 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;
@@ -1830,18 +1831,20 @@ 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);