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

[Amol Grover]

On Wed, Nov 27, 2019 at 10:25:57AM -0500, Joel Fernandes wrote:
> 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 :)

I read-up a few articles about this. I think I've understood the problem. I'm
sending in the ammended patch now. Sorry for this. Won't happen again.

Thanks
Amol

> 
> - Joel