netdev - Re: pull-request: bpf 2022-03-29

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Date:   Thu, 31 Mar 2022 10:12:39 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com>
Subject: Re: pull-request: bpf 2022-03-29

On Wed, 30 Mar 2022 08:09:59 -0700
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Wed, Mar 30, 2022 at 2:15 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >
> > On Wed, 30 Mar 2022 13:52:17 +0900
> > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >
> > > On Tue, 29 Mar 2022 18:51:22 -0700
> > > Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> > >
> > > > On Tue, Mar 29, 2022 at 6:41 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > > > >
> > > > > On Tue, 29 Mar 2022 16:49:24 -0700 Alexei Starovoitov wrote:
> > > > > > Hi David, hi Jakub,
> > > > > >
> > > > > > The following pull-request contains BPF updates for your *net* tree.
> > > > > >
> > > > > > We've added 16 non-merge commits during the last 1 day(s) which contain
> > > > > > a total of 24 files changed, 354 insertions(+), 187 deletions(-).
> > > > > >
> > > > > > The main changes are:
> > > > > >
> > > > > > 1) x86 specific bits of fprobe/rethook, from Masami and Peter.
> > > > > >
> > > > > > 2) ice/xsk fixes, from Maciej and Magnus.
> > > > > >
> > > > > > 3) Various small fixes, from Andrii, Yonghong, Geliang and others.
> > > > >
> > > > > There are some new sparse warnings here that look semi-legit.
> > > > > As in harmless but not erroneous.
> > > >
> > > > Both are new warnings and not due to these patches, right?
> > > >
> > > > > kernel/trace/rethook.c:68:9: error: incompatible types in comparison expression (different address spaces):
> > > > > kernel/trace/rethook.c:68:9:    void ( [noderef] __rcu * )( ... )
> > > > > kernel/trace/rethook.c:68:9:    void ( * )( ... )
> > > > >
> > > > > 66 void rethook_free(struct rethook *rh)
> > > > > 67 {
> > > > > 68         rcu_assign_pointer(rh->handler, NULL);
> > > > > 69
> > > > > 70         call_rcu(&rh->rcu, rethook_free_rcu);
> > > > > 71 }
> > > > >
> > > > > Looks like this should be a WRITE_ONCE() ?
> > > >
> > > > Masami, please take a look.
> > >
> > > Yeah, I think we should make this rcu pointer (and read side must use rcu_dereference())
> > > because this rh->handler becomes the key to disable this rethook.
> > > Let me fix that.
> >
> > Sorry, please ignore this. Since the handler pointed by rh->handler never
> > be removed (unless removed by modules, but this will not happen while
> > the rethook is running), YES, WRITE_ONCE() is enough.
> > Please add below.
> >
> > From 92c9c784458f03900823360981812220ce3c7bf3 Mon Sep 17 00:00:00 2001
> > From: Masami Hiramatsu <mhiramat@...nel.org>
> > Date: Wed, 30 Mar 2022 18:13:42 +0900
> > Subject: [PATCH] rethook: Fix to use WRITE_ONCE() for rethook::handler
> >
> > Since the function pointered by rethook::handler never be removed when
> > the rethook is alive, it doesn't need to use rcu_assign_pointer() to
> > update it. Just use WRITE_ONCE().
> >
> > Reported-by: Alexei Starovoitov <alexei.starovoitov@...il.com>
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> 
> Could you please send it as a proper patch so it registers in patchwork?

Sure, I sent the patch. BTW, I marked it as "bpf" instead of "bpf-next",
was that OK? (It seems bpf-next was not updated yet)

Thank you,

> 
> > ---
> >  kernel/trace/rethook.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> > index ab463a4d2b23..b56833700d23 100644
> > --- a/kernel/trace/rethook.c
> > +++ b/kernel/trace/rethook.c
> > @@ -65,7 +65,7 @@ static void rethook_free_rcu(struct rcu_head *head)
> >   */
> >  void rethook_free(struct rethook *rh)
> >  {
> > -       rcu_assign_pointer(rh->handler, NULL);
> > +       WRITE_ONCE(rh->handler, NULL);
> >
> >         call_rcu(&rh->rcu, rethook_free_rcu);
> >  }
> > --
> > 2.25.1
> > --
> > Masami Hiramatsu <mhiramat@...nel.org>


-- 
Masami Hiramatsu <mhiramat@...nel.org>