mm: softdirty: clear VM_SOFTDIRTY flag inside clear_refs_write() instead of clear_soft_dirty()

clear_refs_write() is called earlier than clear_soft_dirty() and it is
more natural to clear VM_SOFTDIRTY (which belongs to VMA entry but not
PTEs) that early instead of clearing it a way deeper inside call chain.

Signed-off-by: Cyrill Gorcunov <[e-mail]>
Cc: Pavel Emelyanov <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Naoya Horiguchi <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/proc/task_mmu.c

···
 		ptent = pte_file_clear_soft_dirty(ptent);
 	}
 
-	if (vma->vm_flags & VM_SOFTDIRTY)
-		vma->vm_flags &= ~VM_SOFTDIRTY;
-
 	set_pte_at(vma->vm_mm, addr, pte, ptent);
 #endif
 }
···
 
 	if (type == CLEAR_REFS_SOFT_DIRTY) {
 		soft_dirty_cleared = true;
-		pr_warn_once("The pagemap bits 55-60 has changed their meaning! "
-				"See the linux/Documentation/vm/pagemap.txt for details.\n");
+		pr_warn_once("The pagemap bits 55-60 has changed their meaning!"
+			     " See the linux/Documentation/vm/pagemap.txt for "
+			     "details.\n");
 	}
 
 	task = get_proc_task(file_inode(file));
···
 			 *
 			 * Writing 3 to /proc/pid/clear_refs only affects file
 			 * mapped pages.
+			 *
+			 * Writing 4 to /proc/pid/clear_refs affects all pages.
 			 */
 			if (type == CLEAR_REFS_ANON && vma->vm_file)
 				continue;
 			if (type == CLEAR_REFS_MAPPED && !vma->vm_file)
 				continue;
+			if (type == CLEAR_REFS_SOFT_DIRTY) {
+				if (vma->vm_flags & VM_SOFTDIRTY)
+					vma->vm_flags &= ~VM_SOFTDIRTY;
+			}
 			walk_page_range(vma->vm_start, vma->vm_end,
 					&clear_refs_walk);
 		}