netdev - Re: [regression v4.11] 617f01211baf ("8139too: use napi_complete

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Message-ID: <1491590329.10124.86.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Fri, 07 Apr 2017 11:38:49 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [regression v4.11] 617f01211baf ("8139too: use
 napi_complete_done()")

On Fri, 2017-04-07 at 21:17 +0300, Ville Syrjälä wrote:
> Hi,
> 
> My old P3 laptop started to die on me in the middle of larger compile
> jobs (using distcc) after v4.11-rc<something>. I bisected the problem
> to 617f01211baf ("8139too: use napi_complete_done()").
> 
> Unfortunately I wasn't able to capture a full oops as the machine doesn't
> have serial and ramoops failed me. I did get one partial oops on vgacon
> which showed rtl8139_poll() being involved (EIP was around
> _raw_spin_unlock_irqrestore() supposedly), so seems to agree with my
> bisect result.
> 
> So maybe some kind of nasty thing going between the hard irq and
> softirq? Perhaps UP related? I tried to stare at the locking around
> rtl8139_poll() for a while but it looked mostly sane to me.
> 

Thanks a lot for the detective work, I am so sorry for this !

Could you try the following patch ?

I do not really see what could be wrong, the code should run just fine
on UP.

Thanks.

diff --git a/drivers/net/ethernet/realtek/8139too.c b/drivers/net/ethernet/realtek/8139too.c
index 89631753e79962d91456d93b71929af768917da1..cd2dbec331dd796f5296cd378561b3443f231673 100644
--- a/drivers/net/ethernet/realtek/8139too.c
+++ b/drivers/net/ethernet/realtek/8139too.c
@@ -2135,11 +2135,12 @@ static int rtl8139_poll(struct napi_struct *napi, int budget)
 	if (likely(RTL_R16(IntrStatus) & RxAckBits))
 		work_done += rtl8139_rx(dev, tp, budget);
 
-	if (work_done < budget && napi_complete_done(napi, work_done)) {
+	if (work_done < budget) {
 		unsigned long flags;
 
 		spin_lock_irqsave(&tp->lock, flags);
-		RTL_W16_F(IntrMask, rtl8139_intr_mask);
+		if (napi_complete_done(napi, work_done))
+			RTL_W16_F(IntrMask, rtl8139_intr_mask);
 		spin_unlock_irqrestore(&tp->lock, flags);
 	}
 	spin_unlock(&tp->rx_lock);