netdev - Re: [PATCH] mt76: hold RCU lock when calling ieee80211_find_sta_by

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Date:   Fri, 12 Feb 2021 10:20:27 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Felix Fietkau <nbd@....name>, lorenzo.bianconi83@...il.com,
        ryder.lee@...iatek.com, kvalo@...eaurora.org, davem@...emloft.net,
        kuba@...nel.org, matthias.bgg@...il.com
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] mt76: hold RCU lock when calling
 ieee80211_find_sta_by_ifaddr()

On 2/11/21 10:36 PM, Felix Fietkau wrote:
> 
> On 2021-02-12 03:13, Shuah Khan wrote:
>> ieee80211_find_sta_by_ifaddr() must be called under the RCU lock and
>> the resulting pointer is only valid under RCU lock as well.
>>
>> Fix mt76_check_sta() to hold RCU read lock before it calls
>> ieee80211_find_sta_by_ifaddr() and release it when the resulting
>> pointer is no longer needed.
>>
>> This problem was found while reviewing code to debug RCU warn from
>> ath10k_wmi_tlv_parse_peer_stats_info() and a subsequent manual audit
>> of other callers of ieee80211_find_sta_by_ifaddr() that don't hold
>> RCU read lock.
>>
>> Signed-off-by: Shuah Khan <skhan@...uxfoundation.org>
> If I'm not mistaken, this patch is unnecessary. mt76_check_sta is only
> called from mt76_rx_poll_complete, which itself is only called under RCU
> lock.
> 

Yes. You are right. I checked the caller of this routine and didn't
go further up. :)

thanks,
-- Shuah