Re: bitmaps/bitops

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Sun, 2003-03-16 at 01:31, Pete Zaitcev wrote:
> > but the prototype for test_and_set_bit() depends on $(ARCH), and it's
> > not consistent, with the second arg (bitmap address) being one of:
> >   volatile void *
> >   void *
> >   volatile unsigned long *
> 
> It should be unsigned long pointer. I have no idea why
> volatile is still alive. Perhaps Linus can remember why he
> left it in on is386. Other arch maintainers midnlessly ape him
> in this area. I think I even kept his e-mail where he explains
> why volatile has to go.

Several 2.4 drivers assume the test_and_set point is a memory
barrier for locking. Lots of

	if(test_and_set_bit(0, &foo))
	{
		x=foodev->blah

Since its inline code and not a memory barrier otherwise there
is little stop the compile doing

	x=foodev->blah

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