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    Subject[PATCH AUTOSEL 4.14 24/35] mac80211: only warn once on chanctx_conf being NULL
    Date
    From: Yibo Zhao <yiboz@codeaurora.org>

    [ Upstream commit 563572340173865a9a356e6bb02579e6998a876d ]

    In multiple SSID cases, it takes time to prepare every AP interface
    to be ready in initializing phase. If a sta already knows everything it
    needs to join one of the APs and sends authentication to the AP which
    is not fully prepared at this point of time, AP's channel context
    could be NULL. As a result, warning message occurs.

    Even worse, if the AP is under attack via tools such as MDK3 and massive
    authentication requests are received in a very short time, console will
    be hung due to kernel warning messages.

    WARN_ON_ONCE() could be a better way for indicating warning messages
    without duplicate messages to flood the console.

    Johannes: We still need to address the underlying problem, but we
    don't really have a good handle on it yet. Suppress the
    worst side-effects for now.

    Signed-off-by: Zhi Chen <zhichen@codeaurora.org>
    Signed-off-by: Yibo Zhao <yiboz@codeaurora.org>
    [johannes: add note, change subject]
    Signed-off-by: Johannes Berg <johannes.berg@intel.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/mac80211/ieee80211_i.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
    index 894937bcd479..9765a54d7dbe 100644
    --- a/net/mac80211/ieee80211_i.h
    +++ b/net/mac80211/ieee80211_i.h
    @@ -1405,7 +1405,7 @@ ieee80211_get_sband(struct ieee80211_sub_if_data *sdata)
    rcu_read_lock();
    chanctx_conf = rcu_dereference(sdata->vif.chanctx_conf);

    - if (WARN_ON(!chanctx_conf)) {
    + if (WARN_ON_ONCE(!chanctx_conf)) {
    rcu_read_unlock();
    return NULL;
    }
    --
    2.20.1
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