On Mon, May 17, 2010 at 08:01:54AM -0700, Linus Torvalds wrote: > > > On Mon, 17 May 2010, Anton Blanchard wrote: > > > > It turns out this bad code is a result of us defining atomic_t as a > > volatile int. > > Heh. Ok, as you point out in the commit message, I obviously agree with > this patch. "volatile" on data is evil, with the possible exception of > "jiffies" type things. > > So applied. I wonder, Linus, is there a good reason to use volatile for these at all? I asked you about it quite a while back, and IIRC you said it might be OK to remove volatile from bitops, provided that callers were audited (ie. that nobody used bitops on volatile variables). For atomic_read it shouldn't matter unless gcc is *really* bad at it. Ah, for atomic_read, the required semantic is surely ACCESS_ONCE, so that's where the volatile is needed? (maybe it would be clearer to explicitly use ACCESS_ONCE?) The case I was thinking about for bitops was for multiple non-atomic bitops, which would be nice to combine. In reality a lot of performance critical code (like page allocator) bites the bullet and does the open-coded bitwise ops. But it would be nice if that just worked for __set_bit / __clear_bit too. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
