Messages in this thread | | | Date | Thu, 29 Jan 2009 10:39:42 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [PATCH -v2] use per cpu data for single cpu ipi calls |
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On Thu, 29 Jan 2009, Peter Zijlstra wrote: > > Calls with wait=1 are deadlockable when done from within irqs or irq > disabled sections because two cpus could cross ipi each other and stay > waiting.
Sure. But this isn't the "wait=1" case. In the waiting case, we don't need to allocate anything at all, we can just use the stack.
So the only case that matters for interrupts is indeed "wait=0", but that's very much also the case we're talking about.
> That leaves us with the !wait case, which wasn't safe because that > kmalloc could fail, and the fallback was wait, which yields the same > deadlock.
Yes. I agree that the _concept_ of the patch is good. No argument there.
I'm just worried about the details.
> That leaves us with 6 cases, > > root@laptop:/usr/src/linux-2.6# git grep "smp_call_function_single(.*0)"
This misses a _lot_ of cases. What about this one:
kernel/relay.c: err = smp_call_function_single(i,
where you're not seeing if it's a non-waiting one or not (it's a waiting one, but my point is that your grep is missing cases).
Doing
git grep -w smp_call_function_single | grep -v '1);'
is probably more likely to find the cases to look for.
But you're right, I'm still not seeing anything that looks _likely_ to be a problem. But I worry that it's something somebody may want to do.
Linus
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