Am 07.11.2010 16:15, Philippe Gerum wrote: > On Thu, 2010-10-28 at 09:46 +0200, Philippe Gerum wrote: >> On Thu, 2010-10-28 at 09:31 +0200, Jan Kiszka wrote: >>> Am 28.10.2010 07:17, Philippe Gerum wrote: >>>> 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). >>> >>> When you want to support shared IRQs, xnarch_disable_irq is tabu. I >>> suppose you meant some my_device_disable_irqs(). >> >> No, it is perfectly valid provided you made sure that no handler >> remained on the shared list. There is absolutely no reason to keep a >> line unmasked if no device is supposed to be active on it. Hence the >> release sequence described earlier. >> >>> >>>> >>>>> 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. >>> >>> This sounds like it's best discussed based on patches. >>> >> >> Likely, yes. I'll have a look when time allows. > > The following patches implements the teardown approach. The basic idea > is: > - neither break nor improve old setups with legacy I-pipe patches not > providing the revised ipipe_control_irq call. > - fix the SMP race when detaching interrupts.
Looks good. > > The last patch also fixes two other issues: > - do not alter the irq descriptor (e.g. cookie and stats) if the > attachment fails early > - do not set irq affinity before the validity checks, and set it only > for the first handler introduced in the shared list. Separate commits? At least mention it in the change log. Jan
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