All of lore.kernel.org
 help / color / mirror / Atom feed
From: Herbert Xu <herbert@gondor.apana.org.au>
To: David Miller <davem@davemloft.net>
Cc: eric.dumazet@gmail.com, ying.huang@linux.intel.com, lkp@01.org,
	linux-kernel@vger.kernel.org, colin.king@canonical.com,
	fengguang.wu@intel.com, netdev@vger.kernel.org
Subject: [PATCH v2] rhashtable: Kill harmless RCU warning in rhashtable_walk_init
Date: Sat, 19 Dec 2015 10:45:28 +0800	[thread overview]
Message-ID: <20151219024528.GA27814@gondor.apana.org.au> (raw)
In-Reply-To: <20151218.162731.305092674804556753.davem@davemloft.net>

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

  reply	other threads:[~2015-12-19  2:46 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-18  1:39 [lkp] [rhashtable] f9f51b8070: INFO: suspicious RCU usage. ] kernel test robot
2015-12-18  5:34 ` Herbert Xu
2015-12-18  6:24   ` rhashtable: Kill harmless RCU warning in rhashtable_walk_init Herbert Xu
2015-12-18 12:54     ` Eric Dumazet
2015-12-18 13:14       ` Herbert Xu
2015-12-18 21:27         ` David Miller
2015-12-19  2:45           ` Herbert Xu [this message]
2015-12-19  4:42             ` [PATCH v2] " David Miller
2015-12-19  4:47               ` [LKP] " Fengguang Wu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20151219024528.GA27814@gondor.apana.org.au \
    --to=herbert@gondor.apana.org.au \
    --cc=colin.king@canonical.com \
    --cc=davem@davemloft.net \
    --cc=eric.dumazet@gmail.com \
    --cc=fengguang.wu@intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=lkp@01.org \
    --cc=netdev@vger.kernel.org \
    --cc=ying.huang@linux.intel.com \
    --subject='Re: [PATCH v2] rhashtable: Kill harmless RCU warning in rhashtable_walk_init' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.