Re: Possible memory ordering bug in page reclaim?

From: David S. Miller
Date: Sat Oct 15 2005 - 18:07:38 EST

From: Andrea Arcangeli <andrea@xxxxxxx>
Date: Sat, 15 Oct 2005 22:07:01 +0200

> sure see alpha:
> __asm__ __volatile__(
> "1: ldq_l %0,%1\n"
> " addq %0,%3,%2\n"
> " addq %0,%3,%0\n"
> " stq_c %0,%1\n"
> " beq %0,2f\n"
> " mb\n"
> the memory barrier is applied way after the write is visible to other
> cpus, you can even get an irq before the mb and block there for some
> usec.

For atomic operations returning values, there must be a memory
barrier both before and after the atomic operation. This is
defined in Documentation/atomic_ops.txt, so Alpha needs to be
fixed to add a memory barrier at the beginning of these
assembler sequences.
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