On Wed, 6 Dec 2006, Matthew Wilcox wrote: > On Wed, Dec 06, 2006 at 11:29:42AM -0800, Christoph Lameter wrote: > > On Wed, 6 Dec 2006, Matthew Wilcox wrote: > > > > > It's just been pointed out to me that the parisc one isn't safe. > > > > > > <dhowells> imagine variable X is set to 3 > > > <dhowells> CPU A issues cmpxchg(&X, 3, 5) > > > <dhowells> you'd expect that to change X to 5 > > > <dhowells> but what if CPU B assigns 6 to X between cmpxchg reading X > > > and it setting X? > > > > The same could happen with a regular cmpxchg. Cmpxchg changes it to 5 and > > then other cpu performs a store before the next instruction. > > For someone who's advocating use of cmpxchg, it seems you don't > understand its semantics! In the scenario dhowells pointed out, X would > be left set to 5. X should have the value 6 under any legitimate > implementation:
Nope this is a UP implementation. There is no cpu B. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/