On Fri, Dec 18, 2015 at 09:39:22AM +0800, kernel test robot wrote:
> FYI, we noticed the below changes on
>
> https://github.com/0day-ci/linux
> Herbert-Xu/rhashtable-Fix-walker-list-corruption/20151216-164833
> commit f9f51b8070be3e829100614a7372b219723b864f ("rhashtable: Fix walker list
> corruption")
>
>
> [ 8.933376] ===============================
> [ 8.933376] ===============================
> [ 8.934629] [ INFO: suspicious RCU usage. ]
> [ 8.934629] [ INFO: suspicious RCU usage. ]
> [ 8.935941] 4.4.0-rc3-00995-gf9f51b8 #2 Not tainted
> [ 8.935941] 4.4.0-rc3-00995-gf9f51b8 #2 Not tainted
> [ 8.937494] -------------------------------
> [ 8.937494] -------------------------------
> [ 8.938818] lib/rhashtable.c:504 suspicious rcu_dereference_protected()
> usage!
> [ 8.938818] lib/rhashtable.c:504 suspicious rcu_dereference_protected()
> usage!
This is actually a false positive because the new spin lock that
we hold prevents ht->tbl from disappearing under us. So here is
a patch to kill the warning with a comment.
---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_raw and
adding a comment.
Signed-off-by: Herbert Xu <herb...@gondor.apana.org.au>
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index eb9240c..3404b06 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -519,7 +519,11 @@ 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);
+ /* We do not need RCU protection because we hold ht->lock
+ * which guarantees that if we see ht->tbl then it won't
+ * die on us.
+ */
+ iter->walker->tbl = rcu_dereference_raw(ht->tbl);
list_add(&iter->walker->list, &iter->walker->tbl->walkers);
spin_unlock(&ht->lock);
--
Email: Herbert Xu <herb...@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
