Messages in this thread | | | Date | Mon, 11 Dec 2017 14:56:09 -0800 | From | Darren Hart <> | Subject | Re: [PATCH 1/1] futex: futex_wake_op, fix sign_extend32 sign bits |
| |
On Mon, Dec 11, 2017 at 08:37:11AM +0100, Jiri Slaby wrote: > On 12/10/2017, 09:50 PM, Linus Torvalds wrote: > > On Thu, Nov 30, 2017 at 6:35 AM, Jiri Slaby <jslaby@suse.cz> wrote: > >> sign_extend32 counts the sign bit parameter from 0, not from 1. So we > >> have to use "11" for 12th bit, not "12". > > > > This interface is crap. It really doesn't make much sense. I wonder > > how many people have gotten this wrong, but it's hard to tell. > > I tend to agree, because it really surprised me. So at that time I > searched for most (all?) uses of the interface, checked them and all of > them *seem* to be fine. > > > I'm applying this directly to my tree since I didn't see anybody else > > react to it, but the whole pattern worries me. > > > > Also, clearly nobody actually uses the odder corners of futex ops > > anyway. Maybe we should deprecate them entirely? > > > > Jiri, did you notice by testing, or what? > > I noticed it by coincidence while fixing the strace build test failures > -- e78c38f6bdd9 (futex: futex_wake_op, do not fail on invalid op). I > compiled a bit modified futex_atomic_op_inuser in userspace to test the > conversion and the added check and it did not work. > > And yes, somebody (tglx?) noted already that this interface is old and > perhaps unused.
The only use I know of for FUTEX_WAKE_OP is glibc lll_futex_wake_unlock(). and that is limited to a single operation.
At the very least, we need to add a futex_wake_op test to the kselftests, something that's been nagging me for a very long time. There are some 120 different combinations of op and cmp and condition value.
Assuming this isn't urgent, I've added it to my projects list.
-- Darren Hart VMware Open Source Technology Center
| |