Re: [Xen-devel] [PATCH] xen: arm: clear the exclusive monitor on exception return

[Tim Deegan <tim@xxxxxxx>]

At 08:53 +0100 on 19 Jul (1374224014), Ian Campbell wrote:
> On Thu, 2013-07-18 at 17:48 +0100, Tim Deegan wrote:
> > At 09:31 +0100 on 18 Jul (1374139884), Ian Campbell wrote:
> > > As well as atomics our spin unlock (also inherited) is just a plain
> > > store.
> > 
> > Well, we already avoid having locks shared between interrupt/exception
> > handlers and plain code,
> 
> We do? Plain code can use the irqsave/restore variants if it wants to
> coexist with irq handlers which take the same locks, can't they? e.g.
> the gic lock is handled this way... If that's not valid then we might
> have a problem ;-)

Yes, but the irqsave variants are there explicitly to avoid the case
where irq-disabled code touches a spinlock that plain code might be
spinning on.  I guess officially there's nothing stopping irq-disabled
code from _unlocking_ a plain-code spinlock, so this covers that case. :)

Tim.


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