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    SubjectRe: [PATCH] tty: add lockdep annotations
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    On Thu, 2012-05-31 at 11:35 +0200, Eric Dumazet wrote:
    > From: Eric Dumazet <edumazet@google.com>
    >
    > tty_lock_pair() do the right thing to avoid deadlocks, but should
    > instruct LOCKDEP of this to avoid a splat.
    >
    > Signed-off-by: Eric Dumazet <edumazet@google.com>
    > ---
    > Latest Linus tree still hang on my machine, at least this patch removes
    > the lockdep problem...

    About 10% of boots on my machine, and this looks like (hand written)

    general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC
    ...
    RIP : tty_shutdown+0x15/)x70

    Call Trace:

    con_shutdown+0x3e/0x50
    queue_release_one_tty+0x24/0x70
    tty_kref_put+0x28/0x30
    tty_unlock+0x2a/0x60
    tty_open+0x4d8/0x620
    chrdev_open+0xb1/0x1a0
    ...

    Sometime stack is :
    memset()
    alloc_tty_struct
    pty_unix98_install
    tty_init_dev
    ptmx_open
    chrdev_open


    I suspect a refcounting problem, but am not familiar enough with tty
    code....





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