On Fri, Aug 17, 2007 at 01:48:09PM -0500, Corey Minyard wrote:
> Paul E. McKenney wrote:
> >On Fri, Aug 17, 2007 at 09:56:45AM +0200, Peter Zijlstra wrote:
> >
> >>On Thu, 2007-08-16 at 09:01 -0700, Paul E. McKenney wrote:
> >>
> >>>On Thu, Aug 16, 2007 at 04:25:07PM +0200, Peter Zijlstra wrote:
> >>>
> >>>>There seem to be some unbalanced rcu_read_{,un}lock() issues of late,
> >>>>how about doing something like this:
> >>>>
> >>>This will break when rcu_read_lock() and rcu_read_unlock() are invoked
> >>>from NMI/SMI handlers -- the raw_local_irq_save() in lock_acquire() will
> >>>not mask NMIs or SMIs.
> >>>
> >>>One approach would be to check for being in an NMI/SMI handler, and
> >>>to avoid calling lock_acquire() and lock_release() in those cases.
> >>>
> >>It seems:
> >>
> >>#define nmi_enter() do { lockdep_off(); __irq_enter(); } while
> >>(0)
> >>#define nmi_exit() do { __irq_exit(); lockdep_on(); } while (0)
> >>
> >>Should make it all work out just fine. (for NMIs at least, /me fully
> >>ignorant of the workings of SMIs)
> >>
> >
> >Very good point, at least for NMIs on i386 and x86_64. Can't say that I
> >know much about SMIs myself. Or about whatever equivalents to NMIs and
> >SMIs might exist on other platforms. :-/ Of course, the other platforms
> >could be handled by making the RCU lockdep operate only on i386 and x86_64
> >if required.
> >
> >Corey, any advice on SMI handlers? Is there something like nmi_enter()
> >and nmi_exit() that allows disabing lockdep?
> >
> You will certainly need something like nmi_enter() and nmi_exit() for
> SMIs, since they can occur at any time like NMIs. As far as anything
> else, you just have to be extremely careful and remember that it can
> occur anyplace. But you already know that :).
So we would need to create an smi_enter() and smi_exit() an place them
appropriately. Any preferences?
> It would be nice if the PowerPC board vendors would tie watchdog
> pretimeouts and some type of timer into the SMI input. It would make
> debugging certain problems much easier. And all those Marvell bridge
> chips have a watchdog pretimeout and I haven't seen any board vendor
> wire it up :(.
Can't say that I have much influence over them, but I must agree
that debuggability is a very good thing!
Thanx, Paul
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