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>

diff --git a/mm/filemap.c b/mm/filemap.c
index 3d4df44..8ed709a 100644 (file)
--- 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.