It is due to this stuff, in drivers/char/tty_io.c:
/* FIXME! What are the locking issues here? This may me overdoing things..
* this question is especially important now that we've removed the irqlock. */
{
unsigned long flags;
local_irq_save(flags); // FIXME: is this safe?
if (tty->ldisc.flush_buffer)
tty->ldisc.flush_buffer(tty);
if (tty->driver.flush_buffer)
tty->driver.flush_buffer(tty);
if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
tty->ldisc.write_wakeup)
(tty->ldisc.write_wakeup)(tty);
local_irq_restore(flags); // FIXME: is this safe?
}
We end up calling local_bh_enable(), which goes BUG if local interrupts are
disabled. It goes BUG because local_bh_enable() will enable interrupts
unconditionally, therefore calling it with interrupts disabled is deadlocky
and wrong.
So our hand is forced. We have to fix that crap up. I wonder how?
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