Re: 3.14-rc2 XFS backtrace because irqs_disabled.

Al Viro
2014-02-12T21:44:15Z

On Wed, Feb 12, 2014 at 01:32:55PM -0800, Linus Torvalds wrote:
> On Wed, Feb 12, 2014 at 1:14 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > Umm... What if we delay __sigqueue_free()? After all, that's where the
> > fat sucker normally comes from. That way we might get away with much
> > smaller structure on stack...
>
> Sounds like the RightThing(tm) to do to me, and I don't see why it
> wouldn't work.
>
> We'd have to teach each user of "dequeue_signal()" to free the siginfo
> thing. Which shouldn't be too bad - I think we've collected all of
> that into generic code, and there isn't the mass or architecture code
> that knows about these things any more. But there are a few odd
> drivers etc and signalfd. I didn't look at what the lifetimes were.

Only signalfd, AFAICS. And there we'd want to use the same small structure -
it's used in
do {
ret = signalfd_dequeue(ctx, &info, nonblock);
if (unlikely(ret <= 0))
break;
ret = signalfd_copyinfo(siginfo, &info);
if (ret < 0)
break;
siginfo++;
total += ret;
nonblock = 1;
} while (--count);
and using a smaller struct would actually speed the things up - skips one
copying. sigqueue would be freed as soon as we'd done signalfd_copyinfo()
(if not by signalfd_copyinfo() itself).

I'll try to put something along those lines together, if you or Oleg don't
do it first.