afs: Fix mmap

Fix afs_add_open_map() to check that the vnode isn't already on the list
when it adds it.  It's possible that afs_drop_open_mmap() decremented
the cb_nr_mmap counter, but hadn't yet got into the locked section to
remove it.

Also vnode->cb_mmap_link should be initialised, so fix that too.

Fixes: 6e0e99d ("afs: Fix mmap coherency vs 3rd-party changes")
Reported-by: [email protected]
Suggested-by: Marc Dionne <[email protected]>
Signed-off-by: David Howells <[email protected]>
Tested-by: [email protected]
cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]/ # v1
Signed-off-by: Linus Torvalds <[email protected]>

Author: dhowells

fs/afs/file.c

@@ -514,8 +514,9 @@ static void afs_add_open_mmap(struct afs_vnode *vnode)
 	if (atomic_inc_return(&vnode->cb_nr_mmap) == 1) {
 		down_write(&vnode->volume->cell->fs_open_mmaps_lock);
 
-		list_add_tail(&vnode->cb_mmap_link,
-			      &vnode->volume->cell->fs_open_mmaps);
+		if (list_empty(&vnode->cb_mmap_link))
+			list_add_tail(&vnode->cb_mmap_link,
+				      &vnode->volume->cell->fs_open_mmaps);
 
 		up_write(&vnode->volume->cell->fs_open_mmaps_lock);
 	}

fs/afs/super.c

@@ -667,6 +667,7 @@ static void afs_i_init_once(void *_vnode)
 	INIT_LIST_HEAD(&vnode->pending_locks);
 	INIT_LIST_HEAD(&vnode->granted_locks);
 	INIT_DELAYED_WORK(&vnode->lock_work, afs_lock_work);
+	INIT_LIST_HEAD(&vnode->cb_mmap_link);
 	seqlock_init(&vnode->cb_lock);
 }