RfC: fueword(9) and casueword(9)

[Oliver Pinter]

On Tue, Oct 28, 2014 at 4:46 PM, John Baldwin <jhb at freebsd.org> wrote:
> On Monday, October 27, 2014 12:55:57 pm Konstantin Belousov wrote:
>> On Mon, Oct 27, 2014 at 11:17:51AM -0400, John Baldwin wrote:
>> > On Tuesday, October 21, 2014 07:23:06 PM Konstantin Belousov wrote:
>> > > On Wed, Oct 22, 2014 at 01:41:12AM +1100, Bruce Evans wrote:
>> > > > A new API should try to fix these __DEVOLATILE() abominations.  I think it
>> > > > is safe, and even correct, to declare the pointers as volatile const void
>> > > > *, since the functions really can handle volatile data, unlike copyin().
>> > > >
>> > > > Atomic op functions are declared as taking pointers to volatile for
>> > > > similar reasons.  Often they are applied to non-volatile data, but
>> > > > adding a qualifier is type-safe and doesn't cost efficiency since the
>> > > > pointer access is is not known to the compiler.  (The last point is not
>> > > > so clear -- the compiler can see things in the functions since they are
>> > > > inline asm.  fueword() isn't inline so its (in)efficiency is not changed.)
>> > > >
>> > > > The atomic read functions are not declared as taking pointers to const.
>> > > > The __DECONST() abomination might be used to work around this bug.
>> > >
>> > > I prefer to not complicate the fetch(9) KPI due to the mistakes in the
>> > > umtx structures definitions.  I think that it is bug to mark the lock
>> > > words with volatile.  I want the fueword(9) interface to be as much
>> > > similar to fuword(9), in particular, volatile seems to be not needed.
>> >
>> > I agree with Bruce here.  casuword() already accepts volatile.  I also
>> > think umtx is correct in marking the field as volatile.  They are subject
>> > to change without the compiler's knowledge albeit by other threads
>> > rather than signal handlers.  Having them marked volatile doesn't really
>> > matter for the kernel, but the header is also used in userland and is
>> > relevant in sem_new.c, etc.
>>
>> You agree with making fueword() accept volatile const void * as the
>> address ?  Or do you agree with the existence of the volatile type
>> qualifier for the lock field of umtx structures ?
>
> I agree with both (I thought Bruce only asserted the first).
>
>> I definitely do not want to make fueword() different from fuword() in
>> this aspect.  If changing both fueword() and fuword() to take volatile
>> const * address, this should be different patch.
>
> I also agree that fuword() and fueword() should take identical arguments,
> so if this change is made it should be a separate patch (and should include
> suword()).
>
> --
> John Baldwin

Hi Konstantin!

I got this error with clang_complete + vim:

"/usr/data/source/git/opBSD/hardenedBSD.git.opntr/sys/kern/kern_pax.c"
286L, 8326Csem_wait: Operation not supported

                                            sem_wait: Operation not
supported


      Fatal Python error: PyEval_SaveThread: NULL tstate
Vim: Caught deadly signal ABRT
Vim: Finished.
Abort (core dumped)

It's on recent HEAD + HardenedBSD patches, so I must to inspect that
this is caused by hbsd's changes or your.

I don't see this problem on HardenedBSD build, which built on Oct. 23:
[1] FreeBSD 11.0-CURRENT #0 0c61f55(hardened/current/master): Thu Oct
23 09:04:50 CEST 2014
[1]     op at hardenedbsd:/usr/obj/usr/src/sys/HARDENEDBSD amd64

(currently I build a new kernel, which was based before the fueword changes)

If you need help, please ping me.


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