Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1295273

[PATCH v2] rhashtable: Kill harmless RCU warning in rhashtable_walk_init

Show all headers | View raw

On Fri, Dec 18, 2015 at 04:27:31PM -0500, David Miller wrote:
> From: Herbert Xu <herbert@gondor.apana.org.au>
> 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 <ying.huang@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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 <herbert@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 linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [lkp] [rhashtable] f9f51b8070: INFO: suspicious RCU usage. ] Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-18 06:40 +0100
  rhashtable: Kill harmless RCU warning in rhashtable_walk_init Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-18 07:30 +0100
    Re: rhashtable: Kill harmless RCU warning in rhashtable_walk_init Eric Dumazet <eric.dumazet@gmail.com> - 2015-12-18 14:00 +0100
      Re: rhashtable: Kill harmless RCU warning in rhashtable_walk_init Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-18 14:20 +0100
        Re: rhashtable: Kill harmless RCU warning in rhashtable_walk_init David Miller <davem@davemloft.net> - 2015-12-18 22:30 +0100
          [PATCH v2] rhashtable: Kill harmless RCU warning in  rhashtable_walk_init Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-19 03:50 +0100
            Re: [LKP] [PATCH v2] rhashtable: Kill harmless RCU warning in  rhashtable_walk_init Fengguang Wu <fengguang.wu@intel.com> - 2015-12-19 05:50 +0100
            Re: [PATCH v2] rhashtable: Kill harmless RCU warning in  rhashtable_walk_init David Miller <davem@davemloft.net> - 2015-12-19 05:50 +0100

csiph-web