Re: [PATCH 2/2] kvm: mmu: page_track: Fix RCU list API usage

[Paul E. McKenney]

On Thu, Jul 16, 2020 at 05:19:52PM -0700, Dexuan-Linux Cui wrote:
> On Thu, Jul 16, 2020 at 7:47 AM Naresh Kamboju
> <naresh.kamboju@xxxxxxxxxx> wrote:
> >
> > On Sun, 12 Jul 2020 at 21:39, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
> > >
> > > On Sun, Jul 12, 2020 at 06:40:03PM +0530, madhuparnabhowmik10@xxxxxxxxx wrote:
> > > > From: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx>
> > > >
> > > > 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@xxxxxxxxx>
> > >
> > > 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.

I am not seeing this here.  Could you please let us know what compiler
and command-line options you are using to generate this?

							Thanx, Paul