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Date: Wed, 13 May 2009 13:39:39 +0200 From: Wolfgang Grandegger <wg@...ndegger.com> To: Oliver Hartkopp <oliver.hartkopp@...kswagen.de> CC: Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 3/7] [PATCH 3/8] can: CAN Network device driver and Netlink interface Oliver Hartkopp wrote: > Andrew Morton wrote: >> On Tue, 12 May 2009 11:28:00 +0200 Wolfgang Grandegger >> <wg@...ndegger.com> wrote: >> >> >>> +int can_restart_now(struct net_device *dev) >>> +{ >>> + struct can_priv *priv = netdev_priv(dev); >>> + struct net_device_stats *stats = &dev->stats; >>> + struct sk_buff *skb; >>> + struct can_frame *cf; >>> + int err; >>> + >>> + /* Synchronize with dev->hard_start_xmit() */ >>> + netif_tx_lock(dev); >>> + >>> + /* Ensure that no more messages can go out */ >>> + if (netif_carrier_ok(dev)) >>> + netif_carrier_off(dev); >>> + >>> + /* Ensure that no more messages can come in */ >>> + err = priv->do_set_mode(dev, CAN_MODE_STOP); >>> + if (err) >>> + return err; >>> + >>> + /* Now it's save to clean up */ >>> + del_timer_sync(&priv->restart_timer); >>> >> >> This is deadlockable. >> >> It calls del_timer_sync() while holding netif_tx_lock(). But the timer >> handler (can_restart_now()) also takes netif_tx_lock(). So if the >> timer handler is presently running, it's sitting there spinning in >> netif_tx_lock(). And del_timer_sync() is sitting there waiting for the >> timer handler to complete. >> >> >> > > Hi Wolfgang, > > would it be an appropriate solution, just to invoke > > netif_stop_queue() in can_bus_off() > > and invoke > > netif_wake_queue() in can_restart_now() > > ??? > > In a BUSOFF condition we're not able to send CAN frames anyway, so we > can disable the device queue and the we won't need any netif_tx_lock() > right? > > AFAIK this was the original implementation before some of the latest > improvement with the netif_carrier stuff. > > What do you think? The problem is the "manual" restart triggered via the netlink interface, which can occur in the middle of ndo_start_xmit(). Wolfgang. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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