Messages in this thread | | | Date | Wed, 9 May 2012 08:36:11 -0700 | From | Greg KH <> | Subject | Re: Killing the tty lock |
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On Tue, May 08, 2012 at 11:08:29AM -0700, Yinghai Lu wrote: > On Wed, May 2, 2012 at 1:36 PM, Greg KH <gregkh@linuxfoundation.org> wrote: > > On Wed, May 02, 2012 at 11:45:15AM +0100, Alan Cox wrote: > >> > It's mostly pretty "sane", but what is this: > >> > > >> > > +/* > >> > > + * Getting the big tty mutex for a pair of ttys with lock ordering > >> > > + * On a non pty/tty pair tty2 can be NULL which is just fine. > >> > > + */ > >> > > +void __lockfunc tty_lock_pair(struct tty_struct *tty, > >> > > + struct tty_struct *tty2) > >> > > +{ > >> > > + if (tty < tty2) { > >> > > + tty_lock(tty); > >> > > + tty_lock(tty2); > >> > > + } else { > >> > > + if (tty2 && tty2 != tty) > >> > > + tty_lock(tty2); > >> > > + tty_lock(tty); > >> > > + } > >> > > +} > >> > > +EXPORT_SYMBOL(tty_lock_pair); > >> > > + > >> > > +void __lockfunc tty_unlock_pair(struct tty_struct *tty, > >> > > + struct tty_struct *tty2) > >> > > +{ > >> > > + tty_unlock(tty); > >> > > + if (tty2 && tty2 != tty) > >> > > + tty_unlock(tty2); > >> > > +} > >> > > +EXPORT_SYMBOL(tty_unlock_pair); > >> > > >> > for? > >> > >> We need to take locks on a pair of tty devices at the same time in some > >> cases (pty/tty pairs). > > > > Ok. > > > >> > And what's with the comparing of pointers as "<"? How portable is that > >> > really, and how are we supposed to control the memory location of these > >> > structures? > >> > >> You don't need to. The point is that we must lock any arbitrary pair of > >> tty structs in a defined order. Pointer comparisons work just fine for > >> this. The fs layer uses similar logic for inode locking. We only care > >> that for any given pair of objects the lock ordering is consistent. > > > > Ah, ok, that makes more sense, sorry, I didn't understand that. > > looks like some patches from Alan in your tty-next cause dead look...
Yes, Alan is currently working on it... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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