[Devel] [PATCH RHEL8 COMMIT] userfaultfd: wp: don't wake up when doing write protect

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-80.1.2.vz8.3.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-80.1.2.vz8.3.6
------>
commit 854073b5675821831a0a15af6ac309095f48c0e0
Author: Peter Xu <peterx at redhat.com>
Date:   Mon Apr 20 10:34:48 2020 +0300

    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 at redhat.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Reviewed-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
    Cc: Andrea Arcangeli <aarcange at redhat.com>
    Cc: Bobby Powers <bobbypowers at gmail.com>
    Cc: Brian Geffon <bgeffon at google.com>
    Cc: David Hildenbrand <david at redhat.com>
    Cc: Denis Plotnikov <dplotnikov at virtuozzo.com>
    Cc: "Dr . David Alan Gilbert" <dgilbert at redhat.com>
    Cc: Hugh Dickins <hughd at google.com>
    Cc: Jerome Glisse <jglisse at redhat.com>
    Cc: Johannes Weiner <hannes at cmpxchg.org>
    Cc: "Kirill A . Shutemov" <kirill at shutemov.name>
    Cc: Martin Cracauer <cracauer at cons.org>
    Cc: Marty McFadden <mcfadden8 at llnl.gov>
    Cc: Maya Gokhale <gokhale2 at llnl.gov>
    Cc: Mel Gorman <mgorman at suse.de>
    Cc: Mike Kravetz <mike.kravetz at oracle.com>
    Cc: Pavel Emelyanov <xemul at openvz.org>
    Cc: Rik van Riel <riel at redhat.com>
    Cc: Shaohua Li <shli at fb.com>
    Link: http://lkml.kernel.org/r/20200220163112.11409-16-peterx@redhat.com
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-102938
    (cherry picked from commit 23080e2783ba45208795faad124eab0e0bdae85a)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 fs/userfaultfd.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 484cd090f2f6..8d8dadc9a8b1 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1803,6 +1803,7 @@ 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;
@@ -1821,18 +1822,20 @@ 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);