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    SubjectRe: Hangups in n_tty_read()
    On Thu, Jul 16, 2009 at 08:48:46PM +0200, Johannes Weiner wrote:
    > Hello Alan,

    Sorry, misspelt your email address (no copy-paste without pty's ;-)

    > I regularly get hung terminals when ^Cing a foreground process. The
    > terminal won't show any sign of input or output anymore then.
    >
    > Here is an excerpt from sysrq+w:
    >
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] conf S 0000000000000000 0 10946 10888 0x00000000
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] ffff88000e1efd58 0000000000000082 ffff88000e1efcc8 ffffffff8103423b
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] 0000000000004000 0000000000012240 000000000000dc78 ffff880001639240
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] ffff88000e1efce8 ffff880024688000 ffff88002f8651c0 ffff880024688378
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] Call Trace:
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] [<ffffffff8103423b>] ? try_to_wake_up+0x29e/0x2b0
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] [<ffffffff8103423b>] ? try_to_wake_up+0x29e/0x2b0
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] [<ffffffff8134f675>] schedule_timeout+0x26/0x190
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] [<ffffffff811ea909>] n_tty_read+0x496/0x74d
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] [<ffffffff8103424d>] ? default_wake_function+0x0/0xf
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] [<ffffffff811e65a5>] tty_read+0x7d/0xba
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] [<ffffffff8109a33b>] vfs_read+0xab/0x122
    > Jul 16 17:33:10 chigurh kernel: [20907.892444] [<ffffffff8109a476>] sys_read+0x47/0x6f
    >
    > Killing the hung foreground process from another terminal works. But
    > it won't recover the screwed terminal and the terminal does not show
    > any reaction to it (like a prompt) even when the process is gone.
    >
    > I remember one hang without X where the cursor-blinking was still
    > affected by keyboard input.

    Please note that this was in screen, too, so pseudo-terminals here as
    well.

    > Unfortunately, I hadn't had the chance to test if input comes through
    > by blindly executing something disk heavy and watch the LEDs or
    > similar, so I can't say for sure if it's just output or if input is
    > affected as well.
    >
    > First kernel I noticed this with was something past .30. And it
    > certainly happens with Linus' latest.
    >
    > Any idea?
    >
    > Hannes


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