On Wed, Mar 18, 2015 at 02:43:01PM +0100, Quentin Lambert wrote: > > > On 18/03/2015 14:36, Dan Carpenter wrote: > >This changelog still doesn't make sense so I took a look at the code. > > > >tty_ldisc_deref() is an unlock function. So this is a lock ordering > >bug. What makes you think the original ordering was correct? Who > >reported this bug? What are the effects of this bug? > I was the one who introduced the ordering change in the first place. > I am just trying to fix it because although nobody complained I am not > sure of the impact and restoring the previous control flow seems to be the > right thing to do. Your changelog should tell me this stuff. The original code is wrong. We take "spin_lock_irqsave(&ch->ch_lock, flags);" before we do "ld = tty_ldisc_ref(tp);" so we should deref before we unlock. It's normally: lock_outer(); lock_inner(); unlock_inner(); unlock_outer(); On the success path we unlock first then deref and that is a mistake. This kind of change is a bit dangerous though so it requires testing. regards, dan carpenter -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
