Re: 'scheduling while atomic' during ppp connection on and2.6.38

From: Jiri Slaby
Date: Mon Mar 21 2011 - 05:15:51 EST

On 03/20/2011 10:58 PM, Alan Cox wrote:
>> + spin_lock_irqsave(&dc->spin_mutex, flags);
>> if (port->port.count)
>> room = kfifo_avail(&port->fifo_ul);
>> - mutex_unlock(&port->tty_sem);
>> + spin_unlock_irqrestore(&dc->spin_mutex, flags);
> dc->spin_mutex does not protect port->port.count.

Neither port->tty_sem did.

Anyway is the test needed at all? I.e. could
tty->ops->write/chars_in_buffer/ntty_write_room be called with
port->port.count == 0 at all?

And the lock should not as well be needed. Kfifo assures atomicity where
there is only one reader and one writer which should be the case here.
Unless tty->ops->write can be called in parallel. And it should not,
that's what's tty->atomic_write_lock for.

suse labs
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