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

[Jia-Ju Bai]

On 06/01/2017 08:07 AM, Larry Finger wrote:

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

On Wed, 31 May 2017 13:26:43 +0300
Kalle Valo <kv...@codeaurora.org> wrote:

Jia-Ju Bai <baijiaju1...@163.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 <baijiaju1...@163.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.

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 <m...@bu3sch.de>
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 <m...@bu3sch.de>
    Tested-by: Larry Finger <larry.fin...@lwfinger.net>
    Signed-off-by: John W. Linville <linvi...@tuxdriver.com>

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

It is fine to me to fix the bug by porting this former patch.

Thanks,
Jia-Ju Bai