Re: [PATCH] avoid unnecessary cache flushes

[David Mosberger]

>>>>> On Mon, 3 Sep 2001 13:14:36 -0700, Richard Henderson <[e-mail]> said:

  Richard> On Fri, Aug 31, 2001 at 09:18:50PM +1000, Paul Mackerras wrote:
  >> +		if (!test_bit(PG_arch_1, &page->flags)) {
  >> +			__flush_dcache_icache((unsigned long)kmap(page));
  >> +			kunmap(page);
  >> +			set_bit(PG_arch_1, &page->flags);

  Richard> Race.  Use test_and_set_bit.

Nope, the old code is correct: you must turn on PG_arch_1 *after*
flushing the cache.  Yes, you might sometimes double flush, but that's
both safe and rare.

	--david