Messages in this thread | | | Date | Mon, 14 Oct 2019 11:09:45 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH] stop_machine: avoid potential race behaviour |
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On Tue, Oct 08, 2019 at 10:36:37AM +0200, Peter Zijlstra wrote: > On Mon, Oct 07, 2019 at 11:45:36AM +0100, Mark Rutland wrote: > > Both multi_cpu_stop() and set_state() access multi_stop_data::state > > racily using plain accesses. These are subject to compiler > > transformations which could break the intended behaviour of the code, > > and this situation is detected by KCSAN on both arm64 and x86 (splats > > below). > > I really don't think there is anything the compiler can do wrong here. > > That is, I'm thinking I'd like to get this called out as a false-positive.
I agree that in practice, it's very unlikely this would go wrong.
There are some things the compiler could do, e.g. with re-ordering of volatile and plain reads of the same variable:
https://lore.kernel.org/lkml/20191003161233.GB38140@lakrids.cambridge.arm.com/
... and while I agree that's vanishingly unlikely to happen here, I couldn't say how to rule that out without ruling out cases that would actually blow up in practice.
> That said, the patch looks obviously fine and will help with the > validation effort so no real objection there.
Great! Can I take that as an Acked-by?
I assume this should go via the tip tree.
Thanks, Mark.
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