Messages in this thread | | | Date | Sat, 2 Jul 2022 13:38:40 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v4 0/5] cpumask: Fix invalid uniprocessor assumptions |
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On Sat, 2 Jul 2022 18:08:23 +0200 Sander Vanheule <sander@svanheule.net> wrote:
> On uniprocessor builds, it is currently assumed that any cpumask will > contain the single CPU: cpu0. This assumption is used to provide > optimised implementations. > > The current assumption also appears to be wrong, by ignoring the fact > that users can provide empty cpumask-s. This can result in bugs as > explained in [1].
It's a little unkind to send people off to some link to explain the very core issue which this patchset addresses! So I enhanced this paragraph:
: The current assumption also appears to be wrong, by ignoring the fact that : users can provide empty cpumasks. This can result in bugs as explained in : [1] - for_each_cpu() will run one iteration of the loop even when passed : an empty cpumask.
> This series introduces some basic tests, and updates the optimisations > for uniprocessor builds. > > The x86 patch was written after the kernel test robot [2] ran into a > failed build. I have tried to list the files potentially affected by the > changes to cpumask.h, in an attempt to find any other cases that fail on > !SMP. I've gone through some of the files manually, and ran a few cross > builds, but nothing else popped up. I (build) checked about half of the > potientally affected files, but I do not have the resources to do them > all. I hope we can fix other issues if/when they pop up later. > > [1] https://lore.kernel.org/all/20220530082552.46113-1-sander@svanheule.net/ > [2] https://lore.kernel.org/all/202206060858.wA0FOzRy-lkp@intel.com/
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