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Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM

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2017-07-19 16:18+0200, Arnd Bergmann:
> On Wed, Jul 19, 2017 at 4:11 PM, Radim Krčmář <rkrcmar@redhat.com> wrote:
> > 2017-07-19 14:53+0200, Arnd Bergmann:
> >> KVM tries to select 'TASKSTATS', which had additional dependencies:
> >>
> >> warning: (KVM) selects TASKSTATS which has unmet direct dependencies (NET && MULTIUSER)
> >>
> >> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> >> ---
> >
> > Hm, do you know why Kconfig warns instead of propagating the
> > dependencies?
> 
> Kconfig propagates 'depends on' dependencies, but cannot turn a 'select'
> into 'depends on', as those two mean different things.
> 
> Another solution to the problem would be to use 'depends on TASKSTATS'.

Good point, 'select' seems misused here.

There is no reason to depend on TASKSTATS (nor NET+MULTIUSER), we only
suggest to enable it with KVM.  KVM uses sched_info_on() to handle any
any possible resulting configuration, c9aaa8957f20 ("KVM: Steal time
implementation").

KVM would work as intended if 'select' would not enable the option if
its dependencies failed (instead of unconditionally forcing the option).

Is the preferred way to encode it:

  'default y if KVM' in config TASK_DELAY_ACCT
  (that adds a non-local and enigmatic dependency and also needlessly
   expands the possible configuration space)

or

  'select TASKSTATS if NET && MULTIUSER' in config KVM
  (that is going to break when dependencies of TASKSTATS change again)

?

thanks.

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[PATCH 0/8] x86: randconfig warning fixes Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
  [PATCH 3/8] x86: math-emu: avoid bogus -Wint-in-bool-context warning Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    [tip:x86/urgent] x86/fpu/math-emu: Avoid bogus  -Wint-in-bool-context warning tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2017-07-20 12:30 +0200
  [PATCH 5/8] x86: silence build with "make -s" Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    [tip:x86/urgent] x86/build: Silence the build with "make -s" tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2017-07-20 12:40 +0200
  [PATCH 6/8] x86: add MULTIUSER dependency for KVM Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM Radim Krčmář <rkrcmar@redhat.com> - 2017-07-19 16:20 +0200
      Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM Arnd Bergmann <arnd@arndb.de> - 2017-07-19 16:20 +0200
        Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM Radim Krčmář <rkrcmar@redhat.com> - 2017-07-19 18:20 +0200
          Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM Paolo Bonzini <pbonzini@redhat.com> - 2017-07-23 15:50 +0200
  [PATCH 2/8] x86: math-emu: possible uninitialized variable use Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    [tip:x86/urgent] x86/fpu/math-emu: Fix possible uninitialized  variable use tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2017-07-20 12:30 +0200
  [PATCH 1/8] perf/x86: shut up false-positive -Wmaybe-uninitialized warning Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    [tip:x86/urgent] perf/x86: Shut up false-positive  -Wmaybe-uninitialized warning tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2017-07-20 12:30 +0200

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