netdev - Re: mmotm 2010-04-28

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Date:	Mon, 03 May 2010 07:38:57 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Valdis.Kletnieks@...edu
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: mmotm 2010-04-28 - RCU whinges

Le dimanche 02 mai 2010 à 13:46 -0400, Valdis.Kletnieks@...edu a écrit :
> On Wed, 28 Apr 2010 16:53:32 PDT, akpm@...ux-foundation.org said:
> > The mm-of-the-moment snapshot 2010-04-28-16-53 has been uploaded to
> > 
> >    http://userweb.kernel.org/~akpm/mmotm/
> 
> I thought we swatted all these, hit another one...
> 
> [    9.131490] ctnetlink v0.93: registering with nfnetlink.
> [    9.131535]
> [    9.131535] ===================================================
> [    9.131704] [ INFO: suspicious rcu_dereference_check() usage. ]
> [    9.131794] ---------------------------------------------------
> [    9.131883] net/netfilter/nf_conntrack_ecache.c:88 invoked rcu_dereference_check() without protection!
> [    9.131977]
> [    9.131977] other info that might help us debug this:
> [    9.131978]
> [    9.132218]
> [    9.132219] rcu_scheduler_active = 1, debug_locks = 0
> [    9.132434] 1 lock held by swapper/1:
> [    9.132519]  #0:  (nf_ct_ecache_mutex){+.+...}, at: [<ffffffff8148922d>] nf_conntrack_register_notifier+0x1a/0x75
> [    9.132938]
> [    9.132939] stack backtrace:
> [    9.133129] Pid: 1, comm: swapper Tainted: G        W   2.6.34-rc5-mmotm0428 #1
> [    9.133220] Call Trace:
> [    9.133319]  [<ffffffff81064832>] lockdep_rcu_dereference+0xaa/0xb2
> [    9.133410]  [<ffffffff81489250>] nf_conntrack_register_notifier+0x3d/0x75
> [    9.133521]  [<ffffffff81b5a157>] ctnetlink_init+0x71/0xd5
> [    9.133627]  [<ffffffff81b5a0e6>] ? ctnetlink_init+0x0/0xd5
> [    9.133735]  [<ffffffff810001ef>] do_one_initcall+0x59/0x14e
> [    9.133843]  [<ffffffff81b2e68a>] kernel_init+0x144/0x1ce
> [    9.133949]  [<ffffffff81003414>] kernel_thread_helper+0x4/0x10
> [    9.134060]  [<ffffffff81598a40>] ? restore_args+0x0/0x30
> [    9.134196]  [<ffffffff81b2e546>] ? kernel_init+0x0/0x1ce
> [    9.134328]  [<ffffffff81003410>] ? kernel_thread_helper+0x0/0x10
> [    9.134530] ip_tables: (C) 2000-2006 Netfilter Core Team
> [    9.134655] TCP bic registered
> 

Thanks for the report !

We can use rcu_dereference_protected() in those cases.

[PATCH] net: Use rcu_dereference_protected in nf_conntrack_ecache

Writers own nf_ct_ecache_mutex.

Reported-by: Valdis Kletnieks <Valdis.Kletnieks@...edu>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 net/netfilter/nf_conntrack_ecache.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c
index f516961..cdcc764 100644
--- a/net/netfilter/nf_conntrack_ecache.c
+++ b/net/netfilter/nf_conntrack_ecache.c
@@ -85,7 +85,8 @@ int nf_conntrack_register_notifier(struct nf_ct_event_notifier *new)
 	struct nf_ct_event_notifier *notify;
 
 	mutex_lock(&nf_ct_ecache_mutex);
-	notify = rcu_dereference(nf_conntrack_event_cb);
+	notify = rcu_dereference_protected(nf_conntrack_event_cb,
+					   lockdep_is_held(&nf_ct_ecache_mutex));
 	if (notify != NULL) {
 		ret = -EBUSY;
 		goto out_unlock;
@@ -105,7 +106,8 @@ void nf_conntrack_unregister_notifier(struct nf_ct_event_notifier *new)
 	struct nf_ct_event_notifier *notify;
 
 	mutex_lock(&nf_ct_ecache_mutex);
-	notify = rcu_dereference(nf_conntrack_event_cb);
+	notify = rcu_dereference_protected(nf_conntrack_event_cb,
+					   lockdep_is_held(&nf_ct_ecache_mutex));
 	BUG_ON(notify != new);
 	rcu_assign_pointer(nf_conntrack_event_cb, NULL);
 	mutex_unlock(&nf_ct_ecache_mutex);
@@ -118,7 +120,8 @@ int nf_ct_expect_register_notifier(struct nf_exp_event_notifier *new)
 	struct nf_exp_event_notifier *notify;
 
 	mutex_lock(&nf_ct_ecache_mutex);
-	notify = rcu_dereference(nf_expect_event_cb);
+	notify = rcu_dereference_protected(nf_expect_event_cb,
+					   lockdep_is_held(&nf_ct_ecache_mutex));
 	if (notify != NULL) {
 		ret = -EBUSY;
 		goto out_unlock;
@@ -138,7 +141,8 @@ void nf_ct_expect_unregister_notifier(struct nf_exp_event_notifier *new)
 	struct nf_exp_event_notifier *notify;
 
 	mutex_lock(&nf_ct_ecache_mutex);
-	notify = rcu_dereference(nf_expect_event_cb);
+	notify = rcu_dereference_protected(nf_expect_event_cb,
+					   lockdep_is_held(&nf_ct_ecache_mutex));
 	BUG_ON(notify != new);
 	rcu_assign_pointer(nf_expect_event_cb, NULL);
 	mutex_unlock(&nf_ct_ecache_mutex);


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