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configfs: Introduce configfs_dirent_lock

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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>
This commit is contained in:
Louis Rilling
2008-06-16 19:00:58 +02:00
committed by Mark Fasheh
parent fe9f387740
commit 6f61076406
4 changed files with 34 additions and 1 deletions
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3
fs/configfs/configfs_internal.h
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@ -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 @@ struct configfs_dirent {
#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;