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Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock

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On Wed 2016-12-07 23:34:19, Lino Sanfilippo wrote:
> On 07.12.2016 22:43, Lino Sanfilippo wrote:
> > Hi Pavel,
> > 
> > On 07.12.2016 22:37, Pavel Machek wrote:
> >> On Wed 2016-12-07 21:05:38, Lino Sanfilippo wrote:
> >>> The driver uses a private lock for synchronization between the xmit
> >>> function and the xmit completion handler, but since the NETIF_F_LLTX flag
> >>> is not set, the xmit function is also called with the xmit_lock held.
> >>> 
> >>> On the other hand the xmit completion handler first takes the private lock
> >>> and (in case that the tx queue has been stopped) the xmit_lock, leading to
> >>> a reverse locking order and the potential danger of a deadlock.
> >>> 
> >>> Fix this by removing the private lock completely and synchronizing the xmit
> >>> function and completion handler solely by means of the xmit_lock. By doing
> >>> this remove also the now unnecessary double check for a stopped tx queue.
> >>> 
> >> 
> >> FYI, here's modified version. I believe _bh versions are needed, and
> >> I'm testing that version now. (Oh and I also ported it to net-next).
> >> 
> >> It survived 30 minutes of testing so far...
> >> 
> > 
> > First off, thanks for testing.
> > Hmm. I dont understand why _bh would be needed. We call that function from
> > BH context only (napi poll and timer).
> > Any idea?
> > 
> 
> Could this once again be caused by irq coalescing? When the tx queue has been stopped
> the cleanup handler has to wakeup the queue within a certain time span, otherwise the
> watchdog will complain (as it happened in your test). Could you retest this with
> irq coalescing disabled?

I actually had TX coalescing disabled, with

-#define STMMAC_TX_FRAMES       64
+#define STMMAC_TX_FRAMES       0


										Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Remove private locks to avoid possible deadlock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 21:10 +0100
  [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 21:10 +0100
    Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-08 00:20 +0100
      Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-08 21:40 +0100
        Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 23:00 +0100
          Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-08 23:20 +0100
            Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 23:20 +0100
              Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-08 23:50 +0100
        Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-09 00:30 +0100
          Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-09 12:30 +0100
            Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-10 03:30 +0100
  [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 21:10 +0100
    Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-07 22:00 +0100
    Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-07 22:00 +0100
    Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-07 22:40 +0100
      Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 22:50 +0100
        Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-07 23:40 +0100
          Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 00:30 +0100
      Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock David Miller <davem@davemloft.net> - 2016-12-08 00:50 +0100
        Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 15:20 +0100
          Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock David Miller <davem@davemloft.net> - 2016-12-08 16:30 +0100
            Re: [PATCH 2/2] net: ethernet: stmmac: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-08 17:00 +0100

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