Return-path: Received: from mail-oi0-f68.google.com ([209.85.218.68]:32953 "EHLO mail-oi0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750954AbdFAAHS (ORCPT ); Wed, 31 May 2017 20:07:18 -0400 Subject: Re: [PATCH] b43legacy: Fix a sleep-in-atomic bug in b43legacy_op_bss_info_changed To: =?UTF-8?Q?Michael_B=c3=bcsch?= , Kalle Valo Cc: Jia-Ju Bai , netdev@vger.kernel.org, linux-wireless@vger.kernel.org, b43-dev@lists.infradead.org, linux-kernel@vger.kernel.org References: <1496225353-5544-1-git-send-email-baijiaju1990@163.com> <877f0xnwyk.fsf@kamboji.qca.qualcomm.com> <20170531173107.25eeda48@wiggum> From: Larry Finger Message-ID: <284d6d5d-d548-9e05-eafd-a6b521af5a04@lwfinger.net> (sfid-20170601_020746_811126_F04D2D8D) Date: Wed, 31 May 2017 19:07:15 -0500 MIME-Version: 1.0 In-Reply-To: <20170531173107.25eeda48@wiggum> Content-Type: text/plain; charset=windows-1252; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: On 05/31/2017 10:32 AM, Michael B?sch wrote: > On Wed, 31 May 2017 13:26:43 +0300 > Kalle Valo wrote: > >> Jia-Ju Bai 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 >>> --- >>> 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 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 Tested-by: Larry Finger Signed-off-by: John W. Linville 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