Re: [ANNOUNCE] Kernel Janitor's TODO list

David Woodhouse
2001-01-28T17:07:44Z

On Sun, 28 Jan 2001, Manfred Spraul wrote:

> It isn't wrong to call schedule() with disabled interrupts - it's a
> feature ;-)
> Those 10% sleep_on() users that aren't broken use it:
>
> for(;;) {
> cli();
> if(condition)
> break;
> sleep_on(&my_wait_queue);
> sti();
> }

That's valid iff the wake_up() can only happen from an ISR.

> E.g. TIOCMIWAIT in drivers/char/serial.c - a nearly correct sleep_on()
> user.

TIOCMIWAIT does restore_flags() before interruptible_sleep_on(). It's
broken too.

Anyway, if you're feeling pedantic, consider what happens if shutdown() is
called from rs_close() just before sleep_on() is called. Regardless of
whether interrupts are disabled.

> But I doubt that 10% of the sleep_on() users are non-broken...

There are cases where you don't care if you miss a wakeup because you have
a timeout. So it's only suboptimal rather than broken. I did produce a
patch to BUG() in sleep_on if the BKL isn't held, at one point. It was
quite interesting.

> If you remove sleep_on(), then you can disallow calling schedule() with
> disabled local interrupts.

The remaining valid users of sleep_on are mainly filesystems - much fs
code gets called with the BKL held. I expect that to change during 2.5, at
which point sleep_on can be terminated with extreme prejudice.

--
dwmw2