configfs: Introduce configfs_dirent_lock
This patch introduces configfs_dirent_lock spinlock to protect configfs_dirent
traversals against linkage mutations (add/del/move). This will allow
configfs_detach_prep() to avoid locking i_mutexes.
Locking rules for configfs_dirent linkage mutations are the same plus the
requirement of taking configfs_dirent_lock. For configfs_dirent walking, one can
either take appropriate i_mutex as before, or take configfs_dirent_lock.
The spinlock could actually be a mutex, but the critical sections are either
O(1) or should not be too long (default groups walking in last patch).
ChangeLog:
- Clarify the comment on configfs_dirent_lock usage
- Move sd->s_element init before linking the new dirent
- In lseek(), do not release configfs_dirent_lock before the dirent is
relinked.
Signed-off-by: Louis Rilling <Louis.Rilling@kerlabs.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
index cca9860..5a33b58 100644
--- a/fs/configfs/configfs_internal.h
+++ b/fs/configfs/configfs_internal.h
@@ -26,6 +26,7 @@
#include <linux/slab.h>
#include <linux/list.h>
+#include <linux/spinlock.h>
struct configfs_dirent {
atomic_t s_count;
@@ -49,6 +50,8 @@
#define CONFIGFS_USET_DROPPING 0x0100
#define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR)
+extern spinlock_t configfs_dirent_lock;
+
extern struct vfsmount * configfs_mount;
extern struct kmem_cache *configfs_dir_cachep;