[Fwd: Bug: 2.2.12 still hangs PPC after some PPP activity]

[Takashi Oe]

On Wed, 29 Sep 1999, Lou Langholtz wrote:

> What might happen if a driver does:
> 
> save_flags(old_flags);
> cli();
> restore_flags(old_flags);
> save_flags(new_flags);
> cli();
> restore_flags(new_flags);
> /* can't we be interupted here? Assume yes, if so */
> restore_flags(old_flags);
> 
> seems like this might introduce a bug if we could get interrupted after the
> restore of the new_flags but before the second restore of old flags in such a
> way such that the proper state of old_flags could change. I'm not comfortable
> enough though with my understanding of interrupts and driver routines to be
> certain one way or another. To be more specific, consider the case on just a
> single processor system. If this strikes anyone else as a possible race
> condition that could introduce a bug, then this is what we need to fix in
> macserial.c's rs_write routine since this code can potentially happen.

I'm fairly certain it's a bug.  Good spotting.  The last restore_flags()
shouldn't be there.

--- macserial.c.ORIG	Wed Sep 29 02:05:14 1999
+++ macserial.c	Wed Sep 29 02:05:31 1999
@@ -1381,7 +1381,6 @@
 	if (info->xmit_cnt && !tty->stopped && !info->tx_stopped
 	    && !info->tx_active)
 		transmit_chars(info);
-	restore_flags(flags);
 	return ret;
 }


Takashi Oe


** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/