Re: mmotm 2010-04-28 - RCU whinges

From: Eric Dumazet
Date: Mon May 03 2010 - 01:39:21 EST


Le dimanche 02 mai 2010 Ã 13:46 -0400, Valdis.Kletnieks@xxxxxx a Ãcrit :
> On Wed, 28 Apr 2010 16:53:32 PDT, akpm@xxxxxxxxxxxxxxxxxxxx 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@xxxxxx>
Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
---
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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