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

Thomas Gleixner
2009-03-12T10:49:50Z

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,

tglx