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

[Naresh Kamboju]

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

-- 
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https://lkft.linaro.org