Re: [PATCH] neighbour: Move the netdev_put() out of RCU callback

[Zqiang]

> 
> On Fri, Oct 9, 2026 at 2:19 AM Zqiang <qiang.zhang@xxxxxxxxx> wrote:
> 
> > 
> > For builts with CONFIG_NET_DEV_REFCNT_TRACKER=y kernels, netdev_put()
> >  records the caller's stack trace via ref_tracker_free() for debugging
> >  reference leaks. however, the netdev_put() is within pneigh_destroy()
> >  RCU callback, this recorded stack is uninformative, it does not reveal
> >  which code path initiated the deletion.
> > 
> Have you seen pneigh double-free ? What motivates this change ?

Firstly, Apologies for delayed reply.



Actually, I didn't see any double-free happening,  just wanted it to
record a meaningful callstack which on release path.  After all, if double-free
really occurs, the callstack of the RCU callback execution path will not be helpful.


> 
> > 
> > This commit therefore move netdev_put() from the RCU callback into the
> >  caller's process context, and replace call_rcu() with kfree_rcu().
> > 
> >  Fixes: d539d8fbd8fc ("neighbour: Free pneigh_entry after RCU grace period.")
> > 
> Please elaborate why your change is safe in the commit message
> and remove the tag.

Does it refer to using kfree_rcu instead of call_rcu ensures safely ?

Thanks
Zqiang

> 
> > 
> > Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxx>
> > 
> nit: full name
> 
> > 
> > ---
> >  net/core/neighbour.c | 14 ++++----------
> >  1 file changed, 4 insertions(+), 10 deletions(-)
> > 
> >  diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> >  index 6ed8eb075146..4263689fc415 100644
> >  --- a/net/core/neighbour.c
> >  +++ b/net/core/neighbour.c
> >  @@ -818,14 +818,6 @@ int pneigh_create(struct neigh_table *tbl,
> >  return err;
> >  }
> > 
> >  -static void pneigh_destroy(struct rcu_head *rcu)
> >  -{
> >  - struct pneigh_entry *n = container_of(rcu, struct pneigh_entry, rcu);
> >  -
> >  - netdev_put(n->dev, &n->dev_tracker);
> >  - kfree(n);
> >  -}
> >  -
> >  int pneigh_delete(struct neigh_table *tbl, const void *pkey,
> >  struct net_device *dev)
> >  {
> >  @@ -849,7 +841,8 @@ int pneigh_delete(struct neigh_table *tbl, const void *pkey,
> >  if (tbl->pdestructor)
> >  tbl->pdestructor(n);
> > 
> >  - call_rcu(&n->rcu, pneigh_destroy);
> >  + netdev_put(n->dev, &n->dev_tracker);
> >  + kfree_rcu(n, rcu);
> >  return 0;
> >  }
> >  }
> >  @@ -891,7 +884,8 @@ static void pneigh_ifdown(struct neigh_table *tbl, struct net_device *dev,
> >  if (tbl->pdestructor)
> >  tbl->pdestructor(n);
> > 
> >  - call_rcu(&n->rcu, pneigh_destroy);
> >  + netdev_put(n->dev, &n->dev_tracker);
> >  + kfree_rcu(n, rcu);
> >  }
> >  }
> > 
> >  --
> >  2.17.1
> >
>