On Fri, Dec 18, 2015 at 04:27:31PM -0500, David Miller wrote:
> From: Herbert Xu <[email protected]>
> Date: Fri, 18 Dec 2015 21:14:08 +0800
>
> > On Fri, Dec 18, 2015 at 04:54:14AM -0800, Eric Dumazet wrote:
> >>
> >> You can avoid the comment by using the self documented and lockdep
> >> enabled primitive
> >>
> >> iter->walker->tbl = rcu_dereference_protected(ht->tbl,
> >> lockdep_is_held(&ht->lock));
> >
> > That is just gross. I think a comment is much better in this case.
>
> Herbert, this macro was created exactly to handle this situation,
> and this is what we do everywhere else in the tree.
OK.
---8<---
The commit f9f51b8070be3e829100614a7372b219723b864f ("rhashtable:
Fix walker list corruption") causes a suspicious RCU usage warning
because we no longer hold ht->mutex when we dereference ht->tbl.
However, this is a false positive because we now hold ht->lock
which also guarantees that ht->tbl won't disppear from under us.
This patch kills the warning by using rcu_dereference_protected.
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index eb9240c..51282f5 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -519,7 +519,8 @@ int rhashtable_walk_init(struct rhashtable *ht, struct
rhashtable_iter *iter)
return -ENOMEM;
spin_lock(&ht->lock);
- iter->walker->tbl = rht_dereference(ht->tbl, ht);
+ iter->walker->tbl =
+ rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));
list_add(&iter->walker->list, &iter->walker->tbl->walkers);
spin_unlock(&ht->lock);
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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