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    SubjectRe: [PATCH net v2 6/8] forcedeth: Fix a race during rmmod of forcedeth
    Ben,

    Thank you for your comments. I understand this patch needs more work.
    So I am going to remove it from this series for now and work on it in
    isolation.

    Regards,

    On Thu, Nov 3, 2011 at 8:46 PM, Ben Hutchings <bhutchings@solarflare.com> wrote:
    > On Thu, 2011-11-03 at 18:41 -0700, David Decotigny wrote:
    >> From: Salman Qazi <sqazi@google.com>
    >>
    >> The race was between del_timer_sync and nv_do_stats_poll called through
    >> nv_get_ethtool_stats.
    >
    > I don't think so.  nv_close() and nv_get_ethtool_stats() are both called
    > with RTNL held.
    >
    > Calling the timer function from nv_get_ethtool_stats is very likely part
    > of the problem though, so why don't you stop doing that?
    >
    > [...]
    >> diff --git a/drivers/net/ethernet/nvidia/forcedeth.c b/drivers/net/ethernet/nvidia/forcedeth.c
    >> index 0af12a8..7996782 100644
    >> --- a/drivers/net/ethernet/nvidia/forcedeth.c
    >> +++ b/drivers/net/ethernet/nvidia/forcedeth.c
    >> @@ -3937,6 +3937,10 @@ static void nv_poll_controller(struct net_device *dev)
    >>  }
    >>  #endif
    >>
    >> +/* No locking is needed as long as this is in the timer
    >> + * callback.  However, any other callers must call this
    >> + * function with np->lock held.
    >> + */
    >
    > So long as this function is used by all of (1) the timer function (2)
    > the ndo_get_stats implementation (3) the ethtool get_stats
    > implementation, it can most certainly be called concurrently on multiple
    > processors.
    >
    > You could have (2) and (3) return the last polled stats and not poll the
    > hardware themselves, but you would need to use the functions from
    > <linux/u64_stats_sync.h> to avoid word-tearing on 32-bit architectures.
    >
    >>  static void nv_do_stats_poll(unsigned long data)
    >>  {
    >>         struct net_device *dev = (struct net_device *) data;
    >> @@ -4589,12 +4593,17 @@ static int nv_get_sset_count(struct net_device *dev, int sset)
    >>
    >>  static void nv_get_ethtool_stats(struct net_device *dev, struct ethtool_stats *estats, u64 *buffer)
    >>  {
    >> +       unsigned long flags;
    >>         struct fe_priv *np = netdev_priv(dev);
    >>
    >> +       spin_lock_irqsave(&np->lock, flags);
    >> +
    >>         /* update stats */
    >>         nv_do_stats_poll((unsigned long)dev);
    >>
    >>         memcpy(buffer, &np->estats, nv_get_sset_count(dev, ETH_SS_STATS)*sizeof(u64));
    >> +
    >> +       spin_unlock_irqrestore(&np->lock, flags);
    >
    > This function is not called from interrupt context.
    >
    >>  }
    >>
    >>  static int nv_link_test(struct net_device *dev)
    >> @@ -5189,13 +5198,13 @@ static int nv_close(struct net_device *dev)
    >>
    >>         spin_lock_irq(&np->lock);
    >>         np->in_shutdown = 1;
    >> +       del_timer_sync(&np->stats_poll);
    >>         spin_unlock_irq(&np->lock);
    >>         nv_napi_disable(dev);
    >>         synchronize_irq(np->pci_dev->irq);
    >>
    >>         del_timer_sync(&np->oom_kick);
    >>         del_timer_sync(&np->nic_poll);
    >> -       del_timer_sync(&np->stats_poll);
    >>
    >>         netif_stop_queue(dev);
    >>         spin_lock_irq(&np->lock);
    >
    > I don't believe this code movement is helpful.
    >
    > Ben.
    >
    > --
    > Ben Hutchings, Staff Engineer, Solarflare
    > Not speaking for my employer; that's the marketing department's job.
    > They asked us to note that Solarflare product names are trademarked.
    >
    >
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