mm: retire GUP WARN_ON_ONCE that outlived its usefulness

Trinity is now hitting the WARN_ON_ONCE we added in v3.15 commit
cda540ace6a1 ("mm: get_user_pages(write,force) refuse to COW in shared
areas").  The warning has served its purpose, nobody was harmed by that
change, so just remove the warning to generate less noise from Trinity.

Which reminds me of the comment I wrongly left behind with that commit
(but was spotted at the time by Kirill), which has since moved into a
separate function, and become even more obscure: delete it.

Reported-by: Dave Jones <davej@codemonkey.org.uk>
Suggested-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/gup.c b/mm/gup.c
index b64a36175884e07604b0e216bc2d545a2892dcb7..7bf19ffa21999c13fa1f24dc01a6bda77217688c 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -430,10 +430,8 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
                         * Anon pages in shared mappings are surprising: now
                         * just reject it.
                         */
-                       if (!is_cow_mapping(vm_flags)) {
-                               WARN_ON_ONCE(vm_flags & VM_MAYWRITE);
+                       if (!is_cow_mapping(vm_flags))
                                return -EFAULT;
-                       }
                }
        } else if (!(vm_flags & VM_READ)) {
                if (!(gup_flags & FOLL_FORCE))

diff --git a/mm/memory.c b/mm/memory.c
index 93ce37989471174439d8973f19b12e776e218cc3..635451abc8f7c9b84663535678a26a9b0848c89d 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2237,11 +2237,6 @@ static int wp_page_shared(struct mm_struct *mm, struct vm_area_struct *vma,
 
        page_cache_get(old_page);
 
-       /*
-        * Only catch write-faults on shared writable pages,
-        * read-only shared pages can get COWed by
-        * get_user_pages(.write=1, .force=1).
-        */
        if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
                int tmp;