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    SubjectRe: mmotm 2010-04-05-16-09 uploaded
    Valdis.Kletnieks@vt.edu wrote:
    > On Mon, 05 Apr 2010 16:09:45 PDT, akpm@linux-foundation.org said:
    >> The mm-of-the-moment snapshot 2010-04-05-16-09 has been uploaded to
    >>
    >> http://userweb.kernel.org/~akpm/mmotm/
    >
    > Seen in dmesg, 2.6.34-rc2-mmotm0323 didn't do this. Tossing it at all the
    > likely suspects, hopefully somebody will recognize it and save me the
    > bisecting. ;)
    >
    > [ 11.488535] ctnetlink v0.93: registering with nfnetlink.
    > [ 11.488579]
    > [ 11.488579] ===================================================
    > [ 11.489529] [ INFO: suspicious rcu_dereference_check() usage. ]
    > [ 11.489988] ---------------------------------------------------
    > [ 11.490494] net/netfilter/nf_conntrack_ecache.c:88 invoked rcu_dereference_check() without protection!
    > [ 11.491024]
    > [ 11.491024] other info that might help us debug this:
    > [ 11.491025]
    > [ 11.492834]
    > [ 11.492835] rcu_scheduler_active = 1, debug_locks = 0
    > [ 11.494124] 1 lock held by swapper/1:
    > [ 11.494776] #0: (nf_ct_ecache_mutex){+.+...}, at: [<ffffffff8148c606>] nf_conntrack_register_notifier+0x1a/0x76
    > [ 11.495505]

    There are some unnecessary rcu_dereference() calls in the conntrack
    notifier registration and unregistration functions.

    Does this fix it?

    diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c
    index d5a9bcd..849614a 100644
    --- a/net/netfilter/nf_conntrack_ecache.c
    +++ b/net/netfilter/nf_conntrack_ecache.c
    @@ -81,11 +81,9 @@ EXPORT_SYMBOL_GPL(nf_ct_deliver_cached_events);
    int nf_conntrack_register_notifier(struct nf_ct_event_notifier *new)
    {
    int ret = 0;
    - struct nf_ct_event_notifier *notify;

    mutex_lock(&nf_ct_ecache_mutex);
    - notify = rcu_dereference(nf_conntrack_event_cb);
    - if (notify != NULL) {
    + if (nf_conntrack_event_cb != NULL) {
    ret = -EBUSY;
    goto out_unlock;
    }
    @@ -101,11 +99,8 @@ EXPORT_SYMBOL_GPL(nf_conntrack_register_notifier);

    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);
    - BUG_ON(notify != new);
    + BUG_ON(nf_conntrack_event_cb != new);
    rcu_assign_pointer(nf_conntrack_event_cb, NULL);
    mutex_unlock(&nf_ct_ecache_mutex);
    }
    @@ -114,11 +109,9 @@ EXPORT_SYMBOL_GPL(nf_conntrack_unregister_notifier);
    int nf_ct_expect_register_notifier(struct nf_exp_event_notifier *new)
    {
    int ret = 0;
    - struct nf_exp_event_notifier *notify;

    mutex_lock(&nf_ct_ecache_mutex);
    - notify = rcu_dereference(nf_expect_event_cb);
    - if (notify != NULL) {
    + if (nf_expect_event_cb != NULL) {
    ret = -EBUSY;
    goto out_unlock;
    }
    @@ -134,11 +127,8 @@ EXPORT_SYMBOL_GPL(nf_ct_expect_register_notifier);

    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);
    - BUG_ON(notify != new);
    + BUG_ON(nf_expect_event_cb != new);
    rcu_assign_pointer(nf_expect_event_cb, NULL);
    mutex_unlock(&nf_ct_ecache_mutex);
    }
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