On Wed, 31 May 2017 19:07:15 -0500
Larry Finger [off-list ref] wrote:

On 05/31/2017 10:32 AM, Michael Büsch wrote:

quoted

On Wed, 31 May 2017 13:26:43 +0300
Kalle Valo [off-list ref] wrote:
  

quoted

Jia-Ju Bai [off-list ref] writes:
 

quoted

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 <redacted>
---
  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 [off-list ref]
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 [off-list ref]
     Tested-by: Larry Finger [off-list ref]
     Signed-off-by: John W. Linville [off-list ref]

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