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    SubjectTTY Locking bug
    Hi All,

    This has cropped up a few times now. The kernel is based on 786f02b from Linus' tree with a couple of networking
    patches from Eric Dumazet.

    [ 78.262987] =============================================
    [ 78.264262] [ INFO: possible recursive locking detected ]
    [ 78.265386] 3.4.0-07822-g786f02b-dirty #2 Tainted: G C
    [ 78.266257] ---------------------------------------------
    [ 78.267065] plymouthd/214 is trying to acquire lock:
    [ 78.268027] (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff81743777>] tty_lock+0x37/0x80
    [ 78.268892]
    [ 78.268892] but task is already holding lock:
    [ 78.270467] (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff81743777>] tty_lock+0x37/0x80
    [ 78.271244]
    [ 78.271244] other info that might help us debug this:
    [ 78.272837] Possible unsafe locking scenario:
    [ 78.272837]
    [ 78.274420] CPU0
    [ 78.275254] ----
    [ 78.276038] lock(&tty->legacy_mutex);
    [ 78.276818] lock(&tty->legacy_mutex);
    [ 78.277585]
    [ 78.277585] *** DEADLOCK ***
    [ 78.277585]
    [ 78.279856] May be due to missing lock nesting notation
    [ 78.279856]
    [ 78.281407] 2 locks held by plymouthd/214:
    [ 78.282188] #0: (tty_mutex){+.+.+.}, at: [<ffffffff813e2761>] tty_release+0x151/0x4b0
    [ 78.282972] #1: (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff81743777>] tty_lock+0x37/0x80
    [ 78.283745]
    [ 78.283745] stack backtrace:
    [ 78.285291] Pid: 214, comm: plymouthd Tainted: G C 3.4.0-07822-g786f02b-dirty #2
    [ 78.286073] Call Trace:
    [ 78.286875] [<ffffffff810c8ca4>] print_deadlock_bug+0xf4/0x100
    [ 78.287679] [<ffffffff810ca6e4>] validate_chain+0x644/0x720
    [ 78.288465] [<ffffffff810cafed>] __lock_acquire+0x3ad/0x9f0
    [ 78.289258] [<ffffffff810cafed>] ? __lock_acquire+0x3ad/0x9f0
    [ 78.290039] [<ffffffff81022183>] ? native_sched_clock+0x13/0x80
    [ 78.290818] [<ffffffff810221f9>] ? sched_clock+0x9/0x10
    [ 78.291605] [<ffffffff810cbced>] lock_acquire+0x9d/0x200
    [ 78.292378] [<ffffffff81743777>] ? tty_lock+0x37/0x80
    [ 78.293159] [<ffffffff81743777>] ? tty_lock+0x37/0x80
    [ 78.293916] [<ffffffff8173f574>] mutex_lock_nested+0x74/0x380
    [ 78.294671] [<ffffffff81743777>] ? tty_lock+0x37/0x80
    [ 78.295440] [<ffffffff813e2761>] ? tty_release+0x151/0x4b0
    [ 78.296206] [<ffffffff81743777>] tty_lock+0x37/0x80
    [ 78.296961] [<ffffffff817437e3>] tty_lock_pair+0x23/0x5c
    [ 78.297727] [<ffffffff813e276c>] tty_release+0x15c/0x4b0
    [ 78.298485] [<ffffffff811be7ec>] __fput+0xcc/0x290
    [ 78.299250] [<ffffffff811be9d5>] fput+0x25/0x30
    [ 78.299998] [<ffffffff813df553>] tioccons+0xc3/0xd0
    [ 78.300741] [<ffffffff813e36c0>] tty_ioctl+0x560/0x960
    [ 78.301491] [<ffffffff811a3016>] ? kmem_cache_free+0x96/0x260
    [ 78.302211] [<ffffffff812c2710>] ? inode_has_perm.constprop.34+0x30/0x40
    [ 78.302934] [<ffffffff811d0c1a>] do_vfs_ioctl+0x8a/0x340
    [ 78.303667] [<ffffffff812c3c41>] ? selinux_file_ioctl+0x71/0x150
    [ 78.304369] [<ffffffff811d0f61>] sys_ioctl+0x91/0xa0
    [ 78.305057] [<ffffffff8174cc69>] system_call_fastpath+0x16/0x1b

    Thanks,

    Jack


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