• Eric W. Biederman's avatar
    proc: Allow proc_free_inum to be called from any context · dfb2ea45
    Eric W. Biederman authored
    While testing the pid namespace code I hit this nasty warning.
    
    [  176.262617] ------------[ cut here ]------------
    [  176.263388] WARNING: at /home/eric/projects/linux/linux-userns-devel/kernel/softirq.c:160 local_bh_enable_ip+0x7a/0xa0()
    [  176.265145] Hardware name: Bochs
    [  176.265677] Modules linked in:
    [  176.266341] Pid: 742, comm: bash Not tainted 3.7.0userns+ #18
    [  176.266564] Call Trace:
    [  176.266564]  [<ffffffff810a539f>] warn_slowpath_common+0x7f/0xc0
    [  176.266564]  [<ffffffff810a53fa>] warn_slowpath_null+0x1a/0x20
    [  176.266564]  [<ffffffff810ad9ea>] local_bh_enable_ip+0x7a/0xa0
    [  176.266564]  [<ffffffff819308c9>] _raw_spin_unlock_bh+0x19/0x20
    [  176.266564]  [<ffffffff8123dbda>] proc_free_inum+0x3a/0x50
    [  176.266564]  [<ffffffff8111d0dc>] free_pid_ns+0x1c/0x80
    [  176.266564]  [<ffffffff8111d195>] put_pid_ns+0x35/0x50
    [  176.266564]  [<ffffffff810c608a>] put_pid+0x4a/0x60
    [  176.266564]  [<ffffffff8146b177>] tty_ioctl+0x717/0xc10
    [  176.266564]  [<ffffffff810aa4d5>] ? wait_consider_task+0x855/0xb90
    [  176.266564]  [<ffffffff81086bf9>] ? default_spin_lock_flags+0x9/0x10
    [  176.266564]  [<ffffffff810cab0a>] ? remove_wait_queue+0x5a/0x70
    [  176.266564]  [<ffffffff811e37e8>] do_vfs_ioctl+0x98/0x550
    [  176.266564]  [<ffffffff810b8a0f>] ? recalc_sigpending+0x1f/0x60
    [  176.266564]  [<ffffffff810b9127>] ? __set_task_blocked+0x37/0x80
    [  176.266564]  [<ffffffff810ab95b>] ? sys_wait4+0xab/0xf0
    [  176.266564]  [<ffffffff811e3d31>] sys_ioctl+0x91/0xb0
    [  176.266564]  [<ffffffff810a95f0>] ? task_stopped_code+0x50/0x50
    [  176.266564]  [<ffffffff81939199>] system_call_fastpath+0x16/0x1b
    [  176.266564] ---[ end trace 387af88219ad6143 ]---
    
    It turns out that spin_unlock_bh(proc_inum_lock) is not safe when
    put_pid is called with another spinlock held and irqs disabled.
    
    For now take the easy path and use spin_lock_irqsave(proc_inum_lock)
    in proc_free_inum and spin_loc_irq in proc_alloc_inum(proc_inum_lock).
    Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
    dfb2ea45
generic.c 19.2 KB