Messages in this thread | | | Subject | Re: [x86/mm] e2a7dcce31: kernel_BUG_at_arch/x86/mm/tlb.c | From | Arjan van de Ven <> | Date | Tue, 30 May 2017 21:05:01 -0700 |
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On 5/27/2017 9:56 AM, Andy Lutomirski wrote: > On Sat, May 27, 2017 at 9:00 AM, Andy Lutomirski <luto@kernel.org> wrote: >> On Sat, May 27, 2017 at 6:31 AM, kernel test robot >> <xiaolong.ye@intel.com> wrote: >>> >>> FYI, we noticed the following commit: >>> >>> commit: e2a7dcce31f10bd7471b4245a6d1f2de344e7adf ("x86/mm: Rework lazy TLB to track the actual loaded mm") >>> https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git x86/tlbflush_cleanup >> >> Ugh, there's an unpleasant interaction between this patch and >> intel_idle. I suspect that the intel_idle code in question is either >> wrong or pointless, but I want to investigate further. Ingo, can you >> hold off on applying this patch? > > I think this is what's going on: intel_idle has an optimization and > sometimes calls leave_mm(). This is a rather expensive way of working > around x86 Linux's fairly weak lazy mm handling. It also abuses the > whole switch_mm state machine. In particular, there's no guarantee > that the mm is actually lazy at the time. The old code didn't care, > but the new code can oops. > > The short-term fix is to just reorder the code in leave_mm() to avoid the OOPS.
fwiw the reason the code is in intel_idle is to avoid tlb flush IPIs to idle cpus, once the cpu goes into a deep enough idle state. In the current linux code, that is done by no longer having the old TLB live on the CPU, by switching to the neutral kernel-only set of tlbs.
If your proposed changes do that (avoid the IPI/wakeup), great! (if not, there should be a way to do that)
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