[PATCH 3/3] ARM: vfp: Use vfp_lock() in vfp_entry().

[Sebastian Andrzej Siewior]

On 2023-06-27 12:22:23 [+0200], Ard Biesheuvel wrote:
> On Thu, 15 Jun 2023 at 12:17, Sebastian Andrzej Siewior
> <bigeasy at linutronix.de> wrote:
> >
> > vfp_entry() is invoked from exception handler and is fully preemptible.
> > It uses local_bh_disable() to remain uninterrupted while checking the
> > VFP state.
> > This is not working on PREEMPT_RT because local_bh_disable()
> > synchronizes the relevant section but the context remains fully
> > preemptible.
> >
> > Use vfp_lock() for uninterrupted access.
> >
> > VFP_bounce() is invoked from within vfp_entry() and may send a signal.
> > Sending a signal uses spinlock_t which becomes a sleeping lock
> > on PREEMPT_RT and must not be acquired within a preempt-disabled
> > section. Move the vfp_raise_sigfpe() block outside of the
> > preempt-disabled section.
> >
> 
> Isn't the latter a separate issue that predates the softirq changes?
> If so, it should be fixed separately too, and backported to -stable
> (unless nobody uses out-of-tree PREEMPT_RT with those kernels)

This only affects the PREEMPT_RT tree and once this is settled I would
ask to backport the PREEMPT_RT related fixes within the preempt-rt
stable trees and not bother the official stable trees.

Thanks for noting ;)

Sebastian