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

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Lino Sanfilippo <LinoSanfilippo@gmx.de> :
> 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.

netif_tx_stop_queue is used by:
1. xmit function before releasing lock and returning.
2. sxgbe_restart_tx_queue()
   <- sxgbe_tx_interrupt
   <- sxgbe_reset_all_tx_queues()
      <- sxgbe_tx_timeout()

Given xmit won't be called again until tx queue is enabled, it's not clear
how a deadlock could happen due to #1.

Regardless of deadlocks anywhere else, #2 has some serious problem due to
the lack of exclusion between the tx queue restart handler and the xmit
handler.

-- 
Ueimor

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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
  [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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