On Thu, Aug 20, 2015 at 01:17:03AM +0200, Thomas Gleixner wrote: ... > > >> .\" FIXME XXX In discussing errors for FUTEX_CMP_REQUEUE_PI, Darren Hart > > >> .\" made the observation that "EINVAL is returned if the non-pi > > >> .\" to pi or op pairing semantics are violated." > > >> .\" Probably there needs to be a general statement about this > > >> .\" requirement, probably located at about this point in the page. > > >> .\" Darren (or someone else), care to take a shot at this? > > > > > > Well, that's hard to describe because the kernel only has a limited > > > way of detecting such mismatches. It only can detect it when there are > > > non PI waiters on a futex and a PI function is called or vice versa. > > > > Hmmm. Okay, I filed your comments away for reference, but > > hopefully someone can help with some actual text. > > I let Darren come up with something sensible :) Heh, right, no pressure then... I responded to Michael on this recently, copied here for reference: FUTEX_WAIT_REQUEUE_PI can return -EINVAL if called with invalid parameters, such as uaddr==uaddr2, or (in the case of SHARED futexes), the associated keys match (meaning it's the same futex word - shared memory, inode, etc.). This can't happen if the stated policy of requeueing from non-pi to pi is followed as the same word cannot be both non-pi and pi at the same time, requiring them to be unique futex words. FUTEX_CMP_REQUEUE_PI will fail similarly if uaddr and uaddr2 are the same futex word. Also, if nr_wake != 1. But, to the point I was making above, FUTEX_CMP_REQUEUE_PI must requeue uaddr to the same uaddr2 specified in the previous FUTEX_WAIT_REQUEUE_PI call. FUTEX_WAIT_REQUEUE_PI sets up the operation, FUTEX_CMP_REQUEUE_PI completes it, and they must agree on uaddr and uaddr2. Michael, are you still looking for something more from me, or is this FIXME now complete? -- Darren Hart Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
