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Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock

From Lino Sanfilippo <LinoSanfilippo@gmx.de>
Newsgroups linux.kernel
Subject Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock
Date 2016-12-10 03:30 +0100
Message-ID <sMFAd-2G4-5@gated-at.bofh.it> (permalink)
References (1 earlier) <sLQHo-4GV-11@gated-at.bofh.it> <sLTFf-6FW-29@gated-at.bofh.it> <sMdDX-2iT-27@gated-at.bofh.it> <sMgit-3ZR-1@gated-at.bofh.it> <sMrxg-2D4-11@gated-at.bofh.it>
Organization linux.* mail to news gateway

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Hi,

On 09.12.2016 12:21, Pavel Machek wrote:
> On Fri 2016-12-09 00:19:43, Francois Romieu wrote:
>> Lino Sanfilippo <LinoSanfilippo@gmx.de> :
>> [...]
>> > OTOH Pavel said that he actually could produce a deadlock. Now I wonder if
>> > this is caused by that locking scheme (in a way I have not figured out yet)
>> > or if it is a different issue.
>> 
>> stmmac_tx_err races with stmmac_xmit.
> 
> Umm, yes, that looks real.
> 
> And that means that removing tx_lock will not be completely trivial
> :-(. Lino, any ideas there?
> 

Ok, the race is there but it looks like a problem that is not related to 
the use or removal of the private lock.
By a glimpse into other drivers (e.g sky2 or e1000), a possible way to handle a 
tx error is to start a separate task and restart the tx path in that task instead
the irq handler (or timer in case of the watchdog).

In that task we could do:
1. deactivate napi
2. deactivate irqs
3. wait for running napi/irqs do complete (_sync)
4. call stmmac_tx_err()
5. reenable napi
6. reenable irqs

We have to ensure that no xmit() is executing while stmmac_tx_err() does the cleanup,
so stmmac_tx_err() should IMO rather call netif_tx_disable() instead of netif_stop_queue()
(the former grabs the xmit lock before it sets __QUEUE_STATE_DRV_XOFF to disable
the queue).

Regards,
Lino

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Thread

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
              Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-11 21:20 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 20:30 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-15 22:20 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 22:40 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-15 23:40 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-17 18:40 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-18 01:20 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-18 17:20 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 18:30 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 19:40 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Lino Sanfilippo <LinoSanfilippo@gmx.de> - 2016-12-19 23:50 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-18 21:20 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Pavel Machek <pavel@ucw.cz> - 2016-12-19 11:10 +0100
                Re: [PATCH 1/2] net: ethernet: sxgbe: remove private tx queue lock Francois Romieu <romieu@fr.zoreil.com> - 2016-12-20 01:10 +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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