Re: [PATCH v3] net: xfrm: Add '_rcu' tag for rcu protected pointer in netns_xfrm

[Su Yanjun <suyj.fnst@xxxxxxxxxxxxxx>]

On 2019/3/19 23:15, Steffen Klassert wrote:
> On Mon, Mar 18, 2019 at 10:22:46AM -0700, Eric Dumazet wrote:
> > On 03/11/2019 03:10 AM, Steffen Klassert wrote:
> > > On Wed, Mar 06, 2019 at 08:54:08PM -0500, Su Yanjun wrote:
> > > > For rcu protected pointers, we'd better add '__rcu' for them.
> > > >
> > > > Once added '__rcu' tag for rcu protected pointer, the sparse tool reports
> > > > warnings.
> > > >
> > > > net/xfrm/xfrm_user.c:1198:39: sparse:    expected struct sock *sk
> > > > net/xfrm/xfrm_user.c:1198:39: sparse:    got struct sock [noderef] <asn:4> *nlsk
> > > > [...]
> > > >
> > > > So introduce a new wrapper function of nlmsg_unicast  to handle type
> > > > conversions.
> > > >
> > > > This patch also fixes a direct access of a rcu protected socket.
> > > >
> > > > Fixes: be33690d8fcf("[XFRM]: Fix aevent related crash")
> > > > Signed-off-by: Su Yanjun <suyj.fnst@xxxxxxxxxxxxxx>
> > > Patch applied, thanks!
> > Has this patch ever been tested ?
> I had this on your testing system and it did
> not complain. But maybe my testcases did not
> trigger that codepath. Su, can you answer
> on Eric question?
Firs of all, I didn't produce it on my test machine.

Maybe we need recompile the kernel with Eric Dumazet's advise.

CONFIG_LOCKDEP=y
CONFIG_PROVE_RCU=y

The second the code path indeed doesn't do as below:
rcu_read_lock()
rcu_dereference()
...
rcu_read_unlock()

All rcu_dereference are in the follow code path:
xfrm_user_rcv_msg
 link->doit(skb, nlh, attrs)
    rcu_dereference()

I think we can add rcu protection for nlsock

xfrm_user_rcv_msg
  rcu_read_lock()
  link->doit(skb, nlh, attrs)
  rcu_read_unlock()

Any advise?