On Fri, 2010-10-29 at 11:05 +0200, Jan Kiszka wrote: > Am 29.10.2010 10:27, Philippe Gerum wrote: > > On Fri, 2010-10-29 at 09:00 +0200, Jan Kiszka wrote: > >> Am 28.10.2010 21:34, Philippe Gerum wrote: > >>> On Thu, 2010-10-28 at 21:15 +0200, Gilles Chanteperdrix wrote: > >>>> Jan Kiszka wrote: > >>>>> Gilles, > >>>>> > >>>>> I happened to come across rthal_mark_irq_disabled/enabled on arm. On > >>>>> first glance, it looks like these helpers manipulate irq_desc::status > >>>>> non-atomically, i.e. without holding irq_desc::lock. Isn't this fragile? > >>>> > >>>> I have no idea. How do the other architectures do? As far as I know, > >>>> this code has been copied from there. > >>> > >>> Other archs do the same, simply because once an irq is managed by the > >>> hal, it may not be shared in any way with the regular kernel. So locking > >>> is pointless. > >> > >> Indeed, I missed that all the other archs have this uninlined in hal.c. > >> > >> However, this leaves at least a race between xnintr_disable/enable and > >> XN_ISR_PROPAGATE (ie. the related Linux path) behind. > > > > I can't see why XN_ISR_PROPAGATE would be involved here. This service > > pends an interrupt in the pipeline log. > > And this finally lets Linux code run that fiddles with irq_desc::status > as well - potentially in parallel to an unsyncrhonized > xnintr_irq_disable in a different context. That's the problem.
Propagation happens in primary domain. When is this supposed to conflict on the same CPU with linux? > > > > >> Not sure if it > >> matters practically - but risking silent breakage for this micro > >> optimization? > > > > It was not meant as an optimization; we may not grab the linux > > descriptor lock in this context because we may enter it in primary mode. > > Oh, that lock isn't harden as I somehow assumed. This of course > complicates things. > > > > >> Is disabling/enabling really in the highly > >> latency-critical anywhere? Otherwise, I would suggest to just plug this > >> by adding the intended lock for this field. > > > > The caller is expected to manage locking; AFAICS the only one who does > > not is the RTAI skin, which is obsolete and removed in 2.6.x, so no big > > deal. > > The problem is that IRQ forwarding to Linux may let this manipulation > race with plain Linux code, thus has to synchronize with it. It is a > corner case (no one is supposed to pass IRQs down blindly anyway - if at > all), but it should at least be documented ("Don't use disable/enable > together with IRQ forwarding unless you acquire the descriptor lock > properly!"). > > BTW, do we need to track the descriptor state in primary mode at all? > That is the real issue. I don't see the point of doing this with the current kernel code. > Jan > -- Philippe. _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core