[Linux-kernel-mentees] [PATCH] kernel: audit.c: Add __rcu notation to RCU pointer

[Joel Fernandes]

On Wed, Nov 27, 2019 at 12:29 AM Amol Grover <frextrite at gmail.com> wrote:
>
> On Tue, Nov 26, 2019 at 09:29:25PM -0500, Joel Fernandes wrote:
> > On Tue, Nov 26, 2019 at 10:57:23PM +0530, Amol Grover wrote:
> > > add __rcu notation to RCU protected global pointer auditd_conn
> > >
> > > Fixes multiple instances of sparse error:
> > > error: incompatible types in comparison expression
> > > (different address spaces)
> > >
> > > Signed-off-by: Amol Grover <frextrite at gmail.com>
> > > ---
> > >  kernel/audit.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/kernel/audit.c b/kernel/audit.c
> > > index da8dc0db5bd3..30e7fc9b8da2 100644
> > > --- a/kernel/audit.c
> > > +++ b/kernel/audit.c
> > > @@ -102,12 +102,14 @@ struct audit_net {
> > >   * This struct is RCU protected; you must either hold the RCU lock for reading
> > >   * or the associated spinlock for writing.
> > >   */
> > > -static struct auditd_connection {
> > > +struct auditd_connection {
> > >     struct pid *pid;
> > >     u32 portid;
> > >     struct net *net;
> > >     struct rcu_head rcu;
> > > -} *auditd_conn = NULL;
> > > +};
> > > +static struct auditd_connection __rcu *auditd_conn;
> > > +RCU_INIT_POINTER(auditd_conn);
> >
> > Looks like this causes a build error. Always please build test your patches
> > in the very least. And I also did not understand how RCU_INIT_POINTER can
> > even be used outside of a function. In C, executable code cannot be outside
> > functions.
> >
> > Is doing the following not sufficient to fix the sparse issue?
> >
> > thanks,
> >
> >  - Joel
> >
> > ---8<-----------------------
> >
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index 49b6049b26ac..c5d4b5a2dea1 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c
> > @@ -108,8 +108,8 @@ struct auditd_connection {
> >       struct net *net;
> >       struct rcu_head rcu;
> >  };
> > -static struct auditd_connection __rcu *auditd_conn;
> > -RCU_INIT_POINTER(auditd_conn);
> > +static struct auditd_connection __rcu *auditd_conn = NULL;
>
> I ran a quick checkpatch and it gave me this error:
> ERROR: do not initialise statics to NULL
>
> So in order to fix it I decided to INIT the pointer (and failed)

Well, try to understand the checkpatch error then, and do the right thing :)

- Joel