linux-kernel - Re: [PATCH 2/2] kvm: mmu: page

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Date:   Fri, 17 Jul 2020 13:25:26 -0500
From:   Daniel Díaz <daniel.diaz@...aro.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Dexuan-Linux Cui <dexuan.linux@...il.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        madhuparnabhowmik10@...il.com,
        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

The sender of this email would like to recall the message. And drink
more coffee. The sender will also avoid making any more commits on
Friday.

On Fri, 17 Jul 2020 at 13:03, Daniel Díaz <daniel.diaz@...aro.org> wrote:
>
> Hello!
>
> On Fri, 17 Jul 2020 at 12:07, Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > 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@...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
> > > >
> > >
> > > 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?

Please disregard anything below.

Thanks and greetings!

Daniel Díaz
daniel.diaz@...aro.org


> It fails with gcc-8 and gcc-9, but it builds with gcc-10. Quick way to
> reproduce:
>   [host] docker run --rm -it -v /linux:/linux -w /linux
> tuxbuild/build-gcc-9_mips
>   [docker] make ARCH=mips CROSS_COMPILE=mips-linux-gnu- defconfig
>   [docker] make ARCH=mips CROSS_COMPILE=mips-linux-gnu- mm
>
> You can use these other Docker containers: tuxbuild/build-gcc-8_mips
> and tuxbuild/build-gcc-10_mips.
>
> Logs for those builds (and allnoconfig, tinyconfig, with gcc-8, gcc-9
> and gcc-10) can also be found here:
>   https://gitlab.com/Linaro/lkft/kernel-runs/-/jobs/643978135
>
> Greetings!
>
> Daniel Díaz
> daniel.diaz@...aro.org