[PATCH] afs: Fix mmap

[David Howells]

I forgot to commit the patch and so lost part of it.  Full patch below.

David
---
commit 23e7d72edeeff56d7bfa47c32c9638385c90eddd
Author: David Howells <dhowells at redhat.com>
Date:   Mon Dec 13 16:26:44 2021 +0000

    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: 6e0e99d58a65 ("afs: Fix mmap coherency vs 3rd-party changes")
    Reported-by: kafs-testing+fedora34_64checkkafs-build-300 at auristor.com
    Suggested-by: Marc Dionne <marc.dionne at auristor.com>
    Signed-off-by: David Howells <dhowells at redhat.com>
    cc: linux-afs at lists.infradead.org

diff --git a/fs/afs/file.c b/fs/afs/file.c
index cb6ad61eec3b..afe4b803f84b 100644
--- a/fs/afs/file.c
+++ b/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);
 	}
diff --git a/fs/afs/super.c b/fs/afs/super.c
index d110def8aa8e..34c68724c98b 100644
--- a/fs/afs/super.c
+++ b/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);
 }