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SubjectRe: 2.6.14-rc3-rt2

On Thu, 6 Oct 2005, Ingo Molnar wrote:

>
> * Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > Found the problem. You're using a 64 bit machine and flags in the
> > acpi code is defined as u32 and not unsigned long. Ingo's tests put
> > some checks in the flags at the MSBs and these are being truncated.
>
> 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.

-- Steve

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