Messages in this thread | | | Date | Thu, 25 Mar 2010 17:33:59 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] Prevent nested interrupts when the IRQ stack is near overflowing v2 |
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* Ingo Molnar <mingo@elte.hu> wrote:
> > * Linus Torvalds <torvalds@linux-foundation.org> wrote: > > [...] > > > > Now, it's also true that our IRQ infrastructure handlers _could_ be smarter, > > and make the whole problem less likely to happen. > > > > In particular, it's probably true that especially on modern hardware with > > multiple cores, and especially when you do _not_ have irq sharing (which is > > the common case these days for things like network drivers that can use > > MSI), we really would be better off having the irq disabled over the whole > > thing, and on some interrupt controllers it might even be worth it to do the > > old optimization of not masking-and-acking, but just acking. > > Yes. > > > But see above. This is _not_ something that a driver can do any more. They > > don't know whether the interrupt might end up being shared. Just blindly > > setting IRAF_DISABLED in a driver is _not_ the answer. But being smarter in > > the generic irq handler code might work. > > > > And then, what we could do, is to mark the drivers that absolutely _must_ > > be able to nest specially. Like the IDE driver when in PIO mode. Or maybe > > the SCSI drivers, if they still depend on that timer interrupt happening > > while they are busy. > > I think the patch as posted solves a real problem, but also perpetuates a > bad situation. > > At minimum we should print a (one-time) warning that some badness occured. > That would push us either in the direction of improving drivers, or towards > improving the generic code.
Furthermore, applying that patch as-is would not just cause us to do nothing about it in the future, it would also add a rather fragile looking piece of logic. I.e. it's a sweep-under-the-rug thing pretty much IMO.
So i think Thomas is quite right wrt. ugliness of the patch but missed the other important fact that this can occur in a lot of places with high enough IRQ parallelism and cannot be fixed one by one.
Thanks,
Ingo
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