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Date:   Thu, 16 Jul 2020 17:19:52 -0700
From:   Dexuan-Linux Cui <dexuan.linux@...il.com>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     madhuparnabhowmik10@...il.com,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Paolo Bonzini <pbonzini@...hat.com>, rcu@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, kvm list <kvm@...r.kernel.org>,
        frextrite@...il.com, lkft-triage@...ts.linaro.org,
        Dexuan Cui <decui@...rosoft.com>, juhlee@...rosoft.com
Subject: Re: [PATCH 2/2] kvm: mmu: page_track: Fix RCU list API usage

On Thu, Jul 16, 2020 at 7:47 AM Naresh Kamboju
<naresh.kamboju@...aro.org> wrote:
>
> On Sun, 12 Jul 2020 at 21:39, Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > On Sun, Jul 12, 2020 at 06:40:03PM +0530, madhuparnabhowmik10@...il.com wrote:
> > > From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> > >
> > > Use hlist_for_each_entry_srcu() instead of hlist_for_each_entry_rcu()
> > > as it also checkes if the right lock is held.
> > > Using hlist_for_each_entry_rcu() with a condition argument will not
> > > report the cases where a SRCU protected list is traversed using
> > > rcu_read_lock(). Hence, use hlist_for_each_entry_srcu().
> > >
> > > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
> >
> > I queued both for testing and review, thank you!
> >
> > In particular, this one needs an ack by the maintainer.
> >
> >                                                         Thanx, Paul
> >
> > >  arch/x86/kvm/mmu/page_track.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
> > > index a7bcde34d1f2..a9cd17625950 100644
> > > --- a/arch/x86/kvm/mmu/page_track.c
> > > +++ b/arch/x86/kvm/mmu/page_track.c
> > > @@ -229,7 +229,8 @@ void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
> > >               return;
> > >
> > >       idx = srcu_read_lock(&head->track_srcu);
> > > -     hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
> > > +     hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
> > > +                             srcu_read_lock_held(&head->track_srcu))
>
> x86 build failed on linux -next 20200716.
>
> arch/x86/kvm/mmu/page_track.c: In function 'kvm_page_track_write':
> include/linux/rculist.h:727:30: error: left-hand operand of comma
> expression has no effect [-Werror=unused-value]
>   for (__list_check_srcu(cond),     \
>                               ^
> arch/x86/kvm/mmu/page_track.c:232:2: note: in expansion of macro
> 'hlist_for_each_entry_srcu'
>   hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
>   ^~~~~~~~~~~~~~~~~~~~~~~~~
> arch/x86/kvm/mmu/page_track.c: In function 'kvm_page_track_flush_slot':
> include/linux/rculist.h:727:30: error: left-hand operand of comma
> expression has no effect [-Werror=unused-value]
>   for (__list_check_srcu(cond),     \
>                               ^
> arch/x86/kvm/mmu/page_track.c:258:2: note: in expansion of macro
> 'hlist_for_each_entry_srcu'
>   hlist_for_each_entry_srcu(n, &head->track_notifier_list, node,
>   ^~~~~~~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> make[3]: *** [arch/x86/kvm/mmu/page_track.o] Error 1
>
> build link,
> https://ci.linaro.org/view/lkft/job/openembedded-lkft-linux-next/DISTRO=lkft,MACHINE=intel-corei7-64,label=docker-lkft/815/consoleText
>
> --
> Linaro LKFT
> https://lkft.linaro.org

Hi, we're seeing the same building failure with the latest linux-next tree.

Thanks,
Dexuan

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