Re: [PATCH 5/6] futex: unlock before returning -EFAULT

[Darren Hart]

Peter Zijlstra wrote:
> On Thu, 2009-03-12 at 11:47 +0100, Thomas Gleixner wrote:
> > On Thu, 12 Mar 2009, Peter Zijlstra wrote:
> >
> > > On Thu, 2009-03-12 at 00:56 -0700, Darren Hart wrote:
> > > > futex_lock_pi can potentially return -EFAULT with the rt_mutex held.  This
> > > > seems like the wrong thing to do as userspace should assume -EFAULT means the
> > > > lock was not taken.  Even if it could figure this out, we'd be leaving the
> > > > pi_state->owner in an inconsistent state.  This patch unlocks the rt_mutex
> > > > prior to returning -EFAULT to userspace.
> > > lockdep would complain, one is not to leave the kernel with locks held.
> > That would break pi futexes in bits and pieces.
> >
> >      T1 takes F1
> >      T2 blocks on F1
> >      	-> T2 sets up rt_mutex and locks it for T1
> > 	   T2 blocks on rt_mutex and boosts T1
> >
> >      T1 calls a non futex syscall
> >      T1 returns from syscall with the rt_mutex still locked
> >
> > Thanks,
>
> Oh right, raw rt_mutex stuff isn't lockdep annotated, and you use the
> robust futex infrastructure to ensure stuff gets unlocked when holder
> dies. That should work out.

OK, are there any other concerns with this patch?

--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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