Re: 2.6.14-rc3-rt2

[Ingo Molnar <mingo@elte.hu>]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> > ahh ... I would not be surprised if this caused actual problems on x64
> > in the upstream kernel too: using save_flags() over u32 will corrupt a
> > word on the stack ...
> >
> 
> Actually, it's still safe upstream.  The locks are taken via a function
> defined as:
> 
> unsigned long acpi_os_acquire_lock(acpi_handle handle)
> {
> 	unsigned long flags;
> 	spin_lock_irqsave((spinlock_t *) handle, flags);
> 	return flags;
> }
> 
> So a u32 flags with
> 
>   flags = acpi_os_acquire_lock(lock);
> 
> would be safe, unless a 64 bit machine stored the value of IR in the 
> upper word, which I don't know of any archs that do that.

ok. But this still looks very volatile. Nowhere do we guarantee (or can 
we guarantee) that silently zeroing out the upper 32 bits of flags is 
safe!

	Ingo