On Wed, 31 May 2017 19:07:15 -0500
Larry Finger <Larry.Finger@xxxxxxxxxxxx> wrote:
> 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
Damn it :D
> 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.
I'm not sure if it's worth it. There is a risk that this would
introduce new bugs.
But sure, please feel free to try it. This way we can find out how big
this change becomes.
--
Michael
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