linux-kernel - Re: [PATCH] b43legacy: Fix a sleep-in-atomic bug in b43legacy_op_bss_info

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Date:   Wed, 31 May 2017 14:15:47 +0200
From:   Arend van Spriel <arend.vanspriel@...adcom.com>
To:     Kalle Valo <kvalo@...eaurora.org>,
        Jia-Ju Bai <baijiaju1990@....com>
Cc:     Larry.Finger@...inger.net, linux-wireless@...r.kernel.org,
        b43-dev@...ts.infradead.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] b43legacy: Fix a sleep-in-atomic bug in
 b43legacy_op_bss_info_changed

On 31-05-17 12:26, Kalle Valo wrote:
> Jia-Ju Bai <baijiaju1990@....com> writes:
> 
>> The driver may sleep under a spin lock, and the function call path is:
>> b43legacy_op_bss_info_changed (acquire the lock by spin_lock_irqsave)
>>   b43legacy_synchronize_irq
>>     synchronize_irq --> may sleep
>>
>> To fix it, the lock is released before b43legacy_synchronize_irq, and the 
>> lock is acquired again after this function.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
>> ---
>>  drivers/net/wireless/broadcom/b43legacy/main.c |    2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/net/wireless/broadcom/b43legacy/main.c b/drivers/net/wireless/broadcom/b43legacy/main.c
>> index f1e3dad..31ead21 100644
>> --- a/drivers/net/wireless/broadcom/b43legacy/main.c
>> +++ b/drivers/net/wireless/broadcom/b43legacy/main.c
>> @@ -2859,7 +2859,9 @@ static void b43legacy_op_bss_info_changed(struct ieee80211_hw *hw,
>>  	b43legacy_write32(dev, B43legacy_MMIO_GEN_IRQ_MASK, 0);
>>  
>>  	if (changed & BSS_CHANGED_BSSID) {
>> +		spin_unlock_irqrestore(&wl->irq_lock, flags);
>>  		b43legacy_synchronize_irq(dev);
>> +		spin_lock_irqsave(&wl->irq_lock, flags);
> 
> To me this looks like a fragile workaround and not a real fix. You can
> easily add new race conditions with releasing the lock like this.

Hi Jia-Ju,

Agree with Kalle as I was about to say the same thing. You really need
to determine what is protected by the irq_lock. Here you are using the
lock because you are about to change wl->bssid a bit further down. Did
not check the entire function but it seems the lock perimeter is too wide.

Regards,
Arend