FS-Cache: Handle removal of unadded object to the fscache_object_list rb tree

When FS-Cache allocates an object, the following sequence of events can
occur:

 -->fscache_alloc_object()
    -->cachefiles_alloc_object() [via cache->ops->alloc_object]
    <--[returns new object]
    -->fscache_attach_object()
    <--[failed]
    -->cachefiles_put_object() [via cache->ops->put_object]
       -->fscache_object_destroy()
          -->fscache_objlist_remove()
             -->rb_erase() to remove the object from fscache_object_list.

resulting in a crash in the rbtree code.

The problem is that the object is only added to fscache_object_list on
the success path of fscache_attach_object() where it calls
fscache_objlist_add().

So if fscache_attach_object() fails, the object won't have been added to
the objlist rbtree.  We do, however, unconditionally try to remove the
object from the tree.

Thanks to NeilBrown for finding this and suggesting this solution.

Reported-by: NeilBrown <neilb@suse.de>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: (a customer of) NeilBrown <neilb@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
index e1959efad64fa0f4101541683e8c422d27a37aa7..b5ebc2d7d80d30d39b21243561e1f7d26c300329 100644 (file)
--- a/fs/fscache/object-list.c
+++ b/fs/fscache/object-list.c
@@ -50,6 +50,8 @@ void fscache_objlist_add(struct fscache_object *obj)
        struct fscache_object *xobj;
        struct rb_node **p = &fscache_object_list.rb_node, *parent = NULL;
 
+       ASSERT(RB_EMPTY_NODE(&obj->objlist_link));
+
        write_lock(&fscache_object_list_lock);
 
        while (*p) {
@@ -75,6 +77,9 @@ void fscache_objlist_add(struct fscache_object *obj)
  */
 void fscache_objlist_remove(struct fscache_object *obj)
 {
+       if (RB_EMPTY_NODE(&obj->objlist_link))
+               return;
+
        write_lock(&fscache_object_list_lock);
 
        BUG_ON(RB_EMPTY_ROOT(&fscache_object_list));

diff --git a/fs/fscache/object.c b/fs/fscache/object.c
index 53d35c5042404738c213233220500feaf7686ae8..d3b4539f16515451cdd691fd853927d00fa3f8a8 100644 (file)
--- a/fs/fscache/object.c
+++ b/fs/fscache/object.c
@@ -314,6 +314,9 @@ void fscache_object_init(struct fscache_object *object,
        object->cache = cache;
        object->cookie = cookie;
        object->parent = NULL;
+#ifdef CONFIG_FSCACHE_OBJECT_LIST
+       RB_CLEAR_NODE(&object->objlist_link);
+#endif
 
        object->oob_event_mask = 0;
        for (t = object->oob_table; t->events; t++)