[PATCH 4/7] afs: Remove setting of AS_RELEASE_ALWAYS for symlinks and mountpoints

[David Howells]

Regular AFS files correctly use afs_file_aops which have release_folio
set as netfs_release_folio, so AS_RELEASE_ALWAYS is valid for them
when fscache is enabled (set via afs_vnode_set_cache()).
Symlinks and mountpoints in AFS use afs_dir_aops, which does not provide
a release_folio callback. However, afs_apply_status() unconditionally
calls mapping_set_release_always() for these.

In such case when memory management code attempts to release folios,
filemap_release_folio() checks folio_needs_release() which
returns true due to AS_RELEASE_ALWAYS being set. Since there is no
release_folio callback, it falls through to try_to_free_buffers(),
which at present expects buffer_heads to be not null. For symlinks
and mountpoints without buffer_heads, this causes pointer dereference.

Fixes: eae9e78951bb ("afs: Use netfslib for symlinks, allowing them to be cached")
Signed-off-by: Deepakkumar Karn <dkarn@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
---
 fs/afs/inode.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 3f48458694ba..21ac098d03ef 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -126,7 +126,6 @@ static int afs_inode_init_from_status(struct afs_operation *op,
 		}
 		inode->i_mapping->a_ops	= &afs_symlink_aops;
 		inode_nohighmem(inode);
-		mapping_set_release_always(inode->i_mapping);
 		break;
 	default:
 		dump_vnode(vnode, op->file[0].vnode != vnode ? op->file[0].vnode : NULL);