System hang from holding left shift key

[Larry Finger <Larry.Finger@lwfinger.net>]

While absentmindedly holding down the left shift key as I was thinking about my
next input, I froze the keyboard. After 3 seconds, the system sounded a high
beep, and then a low beep after another 3 seconds. At that point, no key entry
had any effect. From the beeps, one might conclude that the input buffer is
full, but a CTRL/U did not clear it. Fortunately, a short press on the power
button shut down the machine cleanly.

I don't know if this is a regression. I found it in v2.6.28-rc2, but the oldest
kernel that I could test (v2.6.24) already has the problem.

When the beeps occur, a stack dump is as follows:

Pid: 2989, comm: Xorg Not tainted 2.6.28-rc2-Linus-00473-g67d1128-dirty #2
Call Trace:
  [<ffffffff803957ce>] kd_mksound+0x69/0xa9
  [<ffffffff8039196c>] vt_ioctl+0x3c4/0x1744
  [<ffffffff8038b097>] tty_ioctl+0x793/0x7fa
  [<ffffffff8025c6c0>] ? trace_hardirqs_off+0xd/0xf
  [<ffffffff8044f94a>] ? _spin_unlock_irqrestore+0x3d/0x4c
  [<ffffffff802bf102>] vfs_ioctl+0x2f/0x7d
  [<ffffffff802bf4fe>] do_vfs_ioctl+0x3ae/0x3e0
  [<ffffffff8020c07c>] ? sysret_check+0x27/0x62
  [<ffffffff802bf577>] sys_ioctl+0x47/0x6a
  [<ffffffff8020c04b>] system_call_fastpath+0x16/0x1b

Thanks,

Larry