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

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Message-ID: <878tlcmixj.fsf@kamboji.qca.qualcomm.com>
Date:   Thu, 01 Jun 2017 07:27:20 +0300
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Michael Büsch <m@...s.ch>
Cc:     Jia-Ju Bai <baijiaju1990@....com>, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, b43-dev@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Larry.Finger@...inger.net
Subject: Re: [PATCH] b43legacy: Fix a sleep-in-atomic bug in b43legacy_op_bss_info_changed

Michael Büsch <m@...s.ch> writes:

>> > --- 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.
>> 
>
>
> I think releasing the lock possibly is fine. It certainly is better than
> sleeping with a lock held.

Sure, but IMHO in general I think the practise of releasing the lock
like this in a middle of function is dangerous as one can easily miss
that upper and lower halves of the function are not actually atomic
anymore. And in this case that it's under a conditional makes it even
worse.

-- 
Kalle Valo