mm: filemap_fault: unique path for locking page

Introduce a single location where filemap_fault() locks the desired page.
There used to be two such places, depending if the initial find_get_page()
was successful or not.

Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Ying Han <yinghan@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 9 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 3d4df44e4221..8ed709a83eb7 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1539,25 +1539,27 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
                  * waiting for the lock.
                  */
                 do_async_mmap_readahead(vma, ra, file, page, offset);
-                lock_page(page);
-
-                /* Did it get truncated? */
-                if (unlikely(page->mapping != mapping)) {
-                        unlock_page(page);
-                        put_page(page);
-                        goto no_cached_page;
-                }
         } else {
                 /* No page in the page cache at all */
                 do_sync_mmap_readahead(vma, ra, file, offset);
                 count_vm_event(PGMAJFAULT);
                 ret = VM_FAULT_MAJOR;
 retry_find:
-                page = find_lock_page(mapping, offset);
+                page = find_get_page(mapping, offset);
                 if (!page)
                         goto no_cached_page;
         }
 
+        lock_page(page);
+
+        /* Did it get truncated? */
+        if (unlikely(page->mapping != mapping)) {
+                unlock_page(page);
+                put_page(page);
+                goto retry_find;
+        }
+        VM_BUG_ON(page->index != offset);
+
         /*
          * We have a locked page in the page cache, now we need to check
          * that it's up-to-date. If not, it is going to be due to an error.