configfs: Make multiple default_group destructions lockdep friendly When destroying a config_group having multiple (nested or not) default groups, lockdep raises a warning because multiple locks of class I_MUTEX_NORMAL are taken in configfs_detach_prep(). This patch makes such default group destructions lockdep-friendly by increasing the i_mutex sub-class from I_MUTEX_CHILD + 1 onwards for each default group locked under a being-destroyed config_group. With this patch and lockdep compiled-in, the number of default groups (whatever their depth in the tree) under a user-created config_group (resp. registered subsystem) is limited to MAX_LOCKDEP_SUBCLASSES - I_MUTEX_CHILD - 1 == 3. This limit is removed when not compiling lockdep. ============================================= [ INFO: possible recursive locking detected ] 2.6.26-rc3 #5 --------------------------------------------- rmdir/1499 is trying to acquire lock: (&sb->s_type->i_mutex_key#11){--..}, at: [] configfs_detach_prep+0x54/0x89 but task is already holding lock: (&sb->s_type->i_mutex_key#11){--..}, at: [] vfs_rmdir+0x49/0xac other info that might help us debug this: 2 locks held by rmdir/1499: #0: (&sb->s_type->i_mutex_key#3/1){--..}, at: [] do_rmdir+0x82/0x108 #1: (&sb->s_type->i_mutex_key#11){--..}, at: [] vfs_rmdir+0x49/0xac stack backtrace: Pid: 1499, comm: rmdir Not tainted 2.6.26-rc3 #5 Call Trace: [] __lock_acquire+0x8d2/0xc78 [] filemap_fault+0x1cf/0x332 [] configfs_detach_prep+0x54/0x89 [] lock_acquire+0x51/0x6c [] configfs_detach_prep+0x54/0x89 [] debug_mutex_lock_common+0x16/0x23 [] mutex_lock_nested+0xcd/0x23b [] configfs_detach_prep+0x54/0x89 [] configfs_rmdir+0xb8/0x1c3 [] vfs_rmdir+0x6b/0xac [] do_rmdir+0xb7/0x108 [] trace_hardirqs_on+0xef/0x113 [] trace_hardirqs_on_thunk+0x35/0x3a [] system_call_after_swapgs+0x7b/0x80 Signed-off-by: Louis Rilling --- fs/configfs/dir.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 66 insertions(+), 8 deletions(-) Index: b/fs/configfs/dir.c =================================================================== --- a/fs/configfs/dir.c 2008-05-22 13:36:06.000000000 +0200 +++ b/fs/configfs/dir.c 2008-05-23 16:46:43.000000000 +0200 @@ -37,16 +37,32 @@ DECLARE_RWSEM(configfs_rename_sem); #ifdef CONFIG_LOCKDEP +static inline int __future_dirent_lock_level(struct configfs_dirent *prev_sd, + struct configfs_dirent *sd) +{ + int lock_level = prev_sd->s_lock_level + 1; + return (lock_level + I_MUTEX_CHILD < MAX_LOCKDEP_SUBCLASSES) ? + lock_level : -ELOOP; +} + +static inline void __set_dirent_lock_level(struct configfs_dirent *sd, + int lock_level) +{ + sd->s_lock_level = lock_level; +} + static inline int set_dirent_lock_level(struct configfs_dirent *prev_sd, struct configfs_dirent *sd) { - int lock_level = prev_sd->s_lock_level + 1; - if (lock_level + I_MUTEX_CHILD < MAX_LOCKDEP_SUBCLASSES) { - sd->s_lock_level = lock_level; - return lock_level; - } - sd->s_lock_level = -1; - return -ELOOP; + int lock_level = __future_dirent_lock_level(prev_sd, sd); + __set_dirent_lock_level(sd, lock_level < 0 ? -1 : lock_level); + return lock_level; +} + +static inline void copy_dirent_lock_level(struct configfs_dirent *from, + struct configfs_dirent *to) +{ + to->s_lock_level = from->s_lock_level; } static inline void reset_dirent_lock_level(struct configfs_dirent *sd) @@ -56,12 +72,28 @@ static inline void reset_dirent_lock_lev #else /* CONFIG_LOCKDEP */ +static inline int __future_dirent_lock_level(struct configfs_dirent *prev_sd, + struct configfs_dirent *sd) +{ + return 0; +} + +static inline void __set_dirent_lock_level(struct configfs_dirent *sd, + int lock_level) +{ +} + static inline int set_dirent_lock_level(struct configfs_dirent *prev_sd, struct configfs_dirent *sd) { return 0; } +static inline void copy_dirent_lock_level(struct configfs_dirent *from, + struct configfs_dirent *to) +{ +} + static inline void reset_dirent_lock_level(struct configfs_dirent *sd) { } @@ -372,6 +404,7 @@ static int configfs_detach_prep(struct d { struct configfs_dirent *parent_sd = dentry->d_fsdata; struct configfs_dirent *sd; + int lock_level; int ret; ret = -EBUSY; @@ -383,7 +416,19 @@ static int configfs_detach_prep(struct d if (sd->s_type & CONFIGFS_NOT_PINNED) continue; if (sd->s_type & CONFIGFS_USET_DEFAULT) { - mutex_lock(&sd->s_dentry->d_inode->i_mutex); + /* Do not set lock_level before we acquire the mutex, + * otherwise a racing mkdir in sd could start from a + * too high lock_level */ + lock_level = __future_dirent_lock_level(parent_sd, sd); + if (lock_level < 0) { + /* Bad bad bad! We cannot remove a directory + * that we let be created! */ + ret = -ELOOP; + break; + } + mutex_lock_nested(&sd->s_dentry->d_inode->i_mutex, + I_MUTEX_CHILD + lock_level); + __set_dirent_lock_level(sd, lock_level); /* Mark that we've taken i_mutex */ sd->s_type |= CONFIGFS_USET_DROPPING; @@ -392,6 +437,10 @@ static int configfs_detach_prep(struct d * deep nesting of default_groups */ ret = configfs_detach_prep(sd->s_dentry); + /* Update parent's lock_level so that remaining + * sibling children keep on globally increasing + * lock_level */ + copy_dirent_lock_level(sd, parent_sd); if (!ret) continue; } else @@ -419,6 +468,7 @@ static void configfs_detach_rollback(str if (sd->s_type & CONFIGFS_USET_DROPPING) { sd->s_type &= ~CONFIGFS_USET_DROPPING; + reset_dirent_lock_level(sd); mutex_unlock(&sd->s_dentry->d_inode->i_mutex); } } @@ -1206,9 +1256,14 @@ static int configfs_rmdir(struct inode * return -EINVAL; } + /* The inode of the config_item being removed is already locked by + * vfs_rmdir() with subclass I_MUTEX_CHILD. Account for it. */ + set_dirent_lock_level(parent_item->ci_dentry->d_fsdata, sd); ret = configfs_detach_prep(dentry); + reset_dirent_lock_level(sd); if (ret) { configfs_detach_rollback(dentry); + reset_dirent_lock_level(sd); config_item_put(parent_item); return ret; } @@ -1492,10 +1547,13 @@ void configfs_unregister_subsystem(struc mutex_lock_nested(&configfs_sb->s_root->d_inode->i_mutex, I_MUTEX_PARENT); + /* Sets subsys's configfs_dirent lock_level to 0 */ + set_dirent_lock_level(configfs_sb->s_root->d_fsdata, dentry->d_fsdata); mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD); if (configfs_detach_prep(dentry)) { printk(KERN_ERR "configfs: Tried to unregister non-empty subsystem!\n"); } + reset_dirent_lock_level(dentry->d_fsdata); configfs_detach_group(&group->cg_item); dentry->d_inode->i_flags |= S_DEAD; mutex_unlock(&dentry->d_inode->i_mutex);