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Date: Tue, 12 Apr 2022 19:34:35 -0700 From: Libo Chen <libo.chen@...cle.com> To: Randy Dunlap <rdunlap@...radead.org>, gregkh@...uxfoundation.org, masahiroy@...nel.org, tglx@...utronix.de, peterz@...radead.org, mingo@...nel.org, vbabka@...e.cz, akpm@...ux-foundation.org Cc: linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org Subject: Re: [PATCH RESEND 1/1] lib/Kconfig: remove DEBUG_PER_CPU_MAPS dependency for CPUMASK_OFFSTACK On 4/12/22 19:13, Randy Dunlap wrote: > Hi, > > On 4/12/22 18:35, Libo Chen wrote: >> Hi Randy, >> >> On 4/12/22 17:18, Randy Dunlap wrote: >>> Hi-- >>> >>> On 4/12/22 16:15, Libo Chen wrote: >>>> Forcing CPUMASK_OFFSTACK to be conditoned on DEBUG_PER_CPU_MAPS doesn't >>>> make a lot of sense nowaday. Even the original patch dating back to 2008, >>>> aab46da0520a ("cpumask: Add CONFIG_CPUMASK_OFFSTACK") didn't give any >>>> rationale for such dependency. >>>> >>>> Nowhere in the code supports the presumption that DEBUG_PER_CPU_MAPS is >>>> necessary for CONFIG_CPUMASK_OFFSTACK. Make no mistake, it's good to >>>> have DEBUG_PER_CPU_MAPS for debugging purpose or precaution, but it's >>>> simply not a hard requirement for CPUMASK_OFFSTACK. Moreover, x86 Kconfig >>>> already can set CPUMASK_OFFSTACK=y without DEBUG_PER_CPU_MAPS=y. >>>> There is no reason other architectures cannot given the fact that they >>>> have even fewer, if any, arch-specific CONFIG_DEBUG_PER_CPU_MAPS code than >>>> x86. >>>> >>>> Signed-off-by: Libo Chen <libo.chen@...cle.com> >>>> --- >>>> lib/Kconfig | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/lib/Kconfig b/lib/Kconfig >>>> index 087e06b4cdfd..7209039dfb59 100644 >>>> --- a/lib/Kconfig >>>> +++ b/lib/Kconfig >>>> @@ -511,7 +511,7 @@ config CHECK_SIGNATURE >>>> bool >>>> config CPUMASK_OFFSTACK >>>> - bool "Force CPU masks off stack" if DEBUG_PER_CPU_MAPS >>> This "if" dependency only controls whether the Kconfig symbol's prompt is >>> displayed (presented) in kconfig tools. Removing it makes the prompt always >>> be displayed. >>> >>> Any architecture could select (should be able to) CPUMASK_OFFSTACK independently >>> of DEBUG_PER_CPU_MAPS. >> Do you mean changing arch/xxxx/Kconfig to select CPUMASK_OFFSTACK under some config xxx? That will work but it requires code changes for each architecture. >> But if you are talking about setting CONFIG_CPUMASK_OFFSTACK=y without CONFIG_DEBUG_PER_CPU_MAPS directly in config file, I have tried, it doesn't work. > I'm just talking about the Kconfig change below. Not talking about whatever else > it might require per architecture. > > But you say you have tried that and it doesn't work. What part of it doesn't work? > The Kconfig part or some code execution? oh the Kconfig part. For example, make olddefconfig on a config file with CPUMASK_OFFSTACK=y only turns off CPUMASK_OFFSTACK unless I explicitly set DEBUG_PER_CPU_MAPS=y Libo > I'll test the Kconfig part of it later (in a few hours). > >> Libo >>> Is there another problem here? >>> >>>> + bool "Force CPU masks off stack" >>>> help >>>> Use dynamic allocation for cpumask_var_t, instead of putting >>>> them on the stack. This is a bit more expensive, but avoids
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