Re: [PATCH/RFC] remove irqs_disabled warning from local_bh_enable

Michael Buesch
2008-06-20T16:19:36Z

On Friday 20 June 2008 18:01:09 Michael Buesch wrote:
> On Friday 20 June 2008 17:55:41 Ingo Molnar wrote:
> >
> > * Michael Buesch <mb@bu3sch.de> wrote:
> >
> > > On Friday 20 June 2008 17:27:48 Ingo Molnar wrote:
> > > > [<c012b361>] local_bh_enable_ip+0xd1/0xe0
> > > > [<c08d9f9f>] _spin_unlock_bh+0x2f/0x40
> > > > [<c0471b92>] vortex_timer+0xe2/0x3e0
> > >
> > > > real bug or false positive?
> > >
> > > Well, a timer runs with IRQs disabled, no? So this would be a bug.
> >
> > indeed - agreed :) [no time for me to fix it, but can test any rfc patch.]
>
> A quick workaround always is to convert the lock into an _irqsafe lock.
> Although it introduces higher overhead (interrupt-wise), it prevents the bug.
> A real fix would require to understand the locking in the driver, which I
> don't, as I never looked at the driver. :)

However, looking at the driver I think the fix actually is trivial:

Index: wireless-testing/drivers/net/3c59x.c
===================================================================
--- wireless-testing.orig/drivers/net/3c59x.c 2008-05-16 00:26:29.000000000 +0200
+++ wireless-testing/drivers/net/3c59x.c 2008-06-20 18:16:55.000000000 +0200
@@ -1768,9 +1768,10 @@ vortex_timer(unsigned long data)
case XCVR_MII: case XCVR_NWAY:
{
ok = 1;
- spin_lock_bh(&vp->lock);
+ /* Interrupts are already disabled */
+ spin_lock(&vp->lock);
vortex_check_media(dev, 0);
- spin_unlock_bh(&vp->lock);
+ spin_unlock(&vp->lock);
}
break;
default: /* Other media types handled by Tx timeouts. */

vp->lock is also taken in hardware IRQ context, so we _have_ to always
use irqsafe locking. As we run in a timer with IRQs disabled,
we can simply use spin_lock.

--
Greetings Michael.