Re: [PATCH] b43legacy: Fix a sleep-in-atomic bug in b43legacy_op_bss_info_changed

[Larry Finger]

On 05/31/2017 10:32 AM, Michael Büsch wrote:
> On Wed, 31 May 2017 13:26:43 +0300
> Kalle Valo <kvalo@xxxxxxxxxxxxxx> wrote:
>
> > Jia-Ju Bai <baijiaju1990@xxxxxxx> 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@xxxxxxx>
> > > ---
> > >   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.
>
>
> I think releasing the lock possibly is fine. It certainly is better than
> sleeping with a lock held.
> We disabled the device interrupts just before this line.
>
> However I think the synchronize_irq should be outside of the
> conditional right after the write to B43legacy_MMIO_GEN_IRQ_MASK. (So
> two lines above)
> I don't think it makes sense to only synchronize if BSS_CHANGED_BSSID
> is set.
>
>
> On the other hand b43 does not have this irq-disabling foobar anymore.
> So somebody must have removed it. Maybe you can find the commit that
> removed this stuff from b43 and port it to b43legacy?
>
>
> So I would vote for moving the synchronize_irq up outside of the
> conditional and put the unlock/lock sequence around it.
> And as a second patch on top of that try to remove this stuff
> altogether like b43 did.

The patch that removed it in b43 is

commit 36dbd9548e92268127b0c31b0e121e63e9207108
Author: Michael Buesch <mb@xxxxxxxxx>
Date:   Fri Sep 4 22:51:29 2009 +0200

    b43: Use a threaded IRQ handler

    Use a threaded IRQ handler to allow locking the mutex and
    sleeping while executing an interrupt.
    This removes usage of the irq_lock spinlock, but introduces
    a new hardirq_lock, which is _only_ used for the PCI/SSB lowlevel
    hard-irq handler. Sleeping busses (SDIO) will use mutex instead.

    Signed-off-by: Michael Buesch <mb@xxxxxxxxx>
    Tested-by: Larry Finger <Larry.Finger@xxxxxxxxxxxx>
    Signed-off-by: John W. Linville <linville@xxxxxxxxxxxxx>

I vaguely remember this patch. Although it is roughly a 1000-line fix, I will 
try to port it to b43legacy. I still have an old BCM4306 PCMCIA card that I can 
test in a PowerBook G4.

I agree with Michael that this is the way to go. Both of Jia-Ju's patches should 
be rejected.

Larry