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    Subject[PATCH 29/30] configfs: dir.c fix possible recursive locking
    Date
    From: Joonwoo Park <joonwpark81@gmail.com>

    configfs_register_subsystem() with default_groups triggers recursive locking.
    it seems that mutex_lock_nested is needed.

    =============================================
    [ INFO: possible recursive locking detected ]
    2.6.24-rc6 #141
    ---------------------------------------------
    swapper/1 is trying to acquire lock:
    (&sb->s_type->i_mutex_key#3){--..}, at: [<c40ca76f>] configfs_attach_group+0x4f/0x190

    but task is already holding lock:
    (&sb->s_type->i_mutex_key#3){--..}, at: [<c40ca9d5>] configfs_register_subsystem+0x55/0x130

    other info that might help us debug this:
    1 lock held by swapper/1:
    #0: (&sb->s_type->i_mutex_key#3){--..}, at: [<c40ca9d5>] configfs_register_subsystem+0x55/0x130

    stack backtrace:
    Pid: 1, comm: swapper Not tainted 2.6.24-rc6 #141
    [<c40053ba>] show_trace_log_lvl+0x1a/0x30
    [<c4005e82>] show_trace+0x12/0x20
    [<c400687e>] dump_stack+0x6e/0x80
    [<c404ec72>] __lock_acquire+0xe62/0x1120
    [<c404efb2>] lock_acquire+0x82/0xa0
    [<c43fdad8>] mutex_lock_nested+0x98/0x2e0
    [<c40ca76f>] configfs_attach_group+0x4f/0x190
    [<c40caa46>] configfs_register_subsystem+0xc6/0x130
    [<c45c8186>] init_netconsole+0x2b6/0x300
    [<c45a75f2>] kernel_init+0x142/0x320
    [<c4004fb3>] kernel_thread_helper+0x7/0x14
    =======================

    Signed-off-by: Joonwoo Park <joonwpark81@gmail.com>
    Signed-off-by: Joel Becker <joel.becker@oracle.com>
    Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
    ---
    fs/configfs/dir.c | 5 +++--
    1 files changed, 3 insertions(+), 2 deletions(-)

    diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
    index 50ed691..a48dc7d 100644
    --- a/fs/configfs/dir.c
    +++ b/fs/configfs/dir.c
    @@ -546,7 +546,7 @@ static int populate_groups(struct config_group *group)
    * That said, taking our i_mutex is closer to mkdir
    * emulation, and shouldn't hurt.
    */
    - mutex_lock(&dentry->d_inode->i_mutex);
    + mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);

    for (i = 0; group->default_groups[i]; i++) {
    new_group = group->default_groups[i];
    @@ -1405,7 +1405,8 @@ int configfs_register_subsystem(struct configfs_subsystem *subsys)
    sd = configfs_sb->s_root->d_fsdata;
    link_group(to_config_group(sd->s_element), group);

    - mutex_lock(&configfs_sb->s_root->d_inode->i_mutex);
    + mutex_lock_nested(&configfs_sb->s_root->d_inode->i_mutex,
    + I_MUTEX_PARENT);

    name.name = group->cg_item.ci_name;
    name.len = strlen(name.name);
    --
    1.5.3.6


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