On Tue, 2010-10-26 at 21:33 +0200, Jan Kiszka wrote: > Am 26.10.2010 07:22, Jan Kiszka wrote: > > Will come up with two patches for stable, one for I-pipe and one for > > Xenomai, later today. Then we can discuss which cases I'm missing. > > While meditating over my approach (which turned out to be less trivial > as expected - of course), I also reconsidered your current patches. The > concerns I had (forwarding of spurious IRQ to Linux) turned out to be > harmless (Linux will ignore such few spurious events). >
That is not even an issue if you consider the sequence to be xnarch_disable_irq then ipipe_control (new version, doing a critical entry to flip the irq mode). > Still, the approach to sync via shutting down the line for the current > domain before xnintr_irq_detach doesn't work for us. It only works if > xnintr_irq_detach actually detaches from the line, but it breaks if > there are users remaining. > > We need intrlock to check if we are the last user while removing > ourselves from the list. And we cannot postpone line detaching after the > critical section as we may otherwise race with the next registration on > that line. IOW, I don't see how to solve the issue without moving the > drain after the detach and making the detach safer instead. > > Do you agree? > I agree this is not trivial, for sure. To keep things simple, I would introduce a new "teardown" flag to freeze the descriptor, thus avoiding further attachments, while xnintr_detach can probe the shared list for lingering users, and eventually call xnarch_disable_irq +xnarch_ignore_irq+xnarch_release_irq in sequence with all locks dropped, if empty. The only adverse effect I can see ATM would be some concurrent caller of xnintr_detach() blocked on the teardown flag on another CPU, albeit it _could_ have joined the bandwagon, attaching the irq, in case the shared list proved to remain active (and thus xnarch_release_irq was not called). But this may also look like a simple way to prevent live locking of interrupt descriptors. YMMV. > Jan > -- Philippe. _______________________________________________ Xenomai-help mailing list [email protected] https://mail.gna.org/listinfo/xenomai-help
