Messages in this thread |  | | Date | Tue, 17 Dec 2019 10:51:56 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] smp: Allow smp_call_function_single_async() to insert locked csd |
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On Mon, Dec 16, 2019 at 03:58:33PM -0500, Peter Xu wrote: > On Mon, Dec 16, 2019 at 09:37:05PM +0100, Peter Zijlstra wrote: > > On Wed, Dec 11, 2019 at 11:29:25AM -0500, Peter Xu wrote:
> > > (3) Others: > > > > > > *** arch/mips/kernel/process.c: > > > raise_backtrace[713] smp_call_function_single_async(cpu, csd); > > > > per-cpu csd data, seems perfectly fine usage. > > I'm not sure whether I get the point, I just feel like it could still > trigger as long as we do it super fast, before IPI handled, > disregarding whether it's per-cpu csd or not.
No, I wasn't paying attention last night. I'm thinking this one might maybe be in 1). It does the state check using that bitmap.
> > > *** arch/x86/kernel/cpuid.c: > > > cpuid_read[85] err = smp_call_function_single_async(cpu, &csd); > > > *** arch/x86/lib/msr-smp.c: > > > rdmsr_safe_on_cpu[182] err = smp_call_function_single_async(cpu, &csd); > > > > These two have csd on stack and wait with a completion. seems fine. > > Yeh this is true, then I'm confused why they don't use the sync() > helpers..
I suspect to be nice for virt. Both CPUID and MSR accesses can trap. but now I'm confused, because it is mostly WRMSR that traps.
Anyway, see the commit here: 07cde313b2d2 ("x86/msr: Allow rdmsr_safe_on_cpu() to schedule")
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