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Date:   Fri, 11 Sep 2020 15:30:41 +0530
From:   Allen <allen.lkml@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     jes@...ined-monkey.org, Jakub Kicinski <kuba@...nel.org>,
        dougmill@...ux.ibm.com, cooldavid@...ldavid.org,
        mlindner@...vell.com, stephen@...workplumber.org,
        borisp@...lanox.com, netdev@...r.kernel.org,
        Romain Perier <romain.perier@...il.com>
Subject: Re: [PATCH v2 01/20] ethernet: alteon: convert tasklets to use new
 tasklet_setup() API

> >> >
> >> >
> >> > -static void ace_tasklet(unsigned long arg)
> >> > +static void ace_tasklet(struct tasklet_struct *t)
> >> >  {
> >> > -     struct net_device *dev = (struct net_device *) arg;
> >> > -     struct ace_private *ap = netdev_priv(dev);
> >> > +     struct ace_private *ap = from_tasklet(ap, t, ace_tasklet);
> >> > +     struct net_device *dev = (struct net_device *)((char *)ap -
> >> > +                             ALIGN(sizeof(struct net_device), NETDEV_ALIGN));
> >> >       int cur_size;
> >> >
> >>
> >> I don't see this is as an improvement.  The 'dev' assignment looks so
> >> incredibly fragile and exposes so many internal details about netdev
> >> object allocation, alignment, and layout.
> >>
> >> Who is going to find and fix this if someone changes how netdev object
> >> allocation works?
> >>
> >
> > Thanks for pointing it out. I'll see if I can fix it to keep it simple.
>
> Just add a backpointer to the netdev from the netdev_priv() if you
> absolutely have too.
>

How does this look?
diff --git a/drivers/net/ethernet/alteon/acenic.c
b/drivers/net/ethernet/alteon/acenic.c
index 8470c836fa18..1a7e4df9b3e9 100644
--- a/drivers/net/ethernet/alteon/acenic.c
+++ b/drivers/net/ethernet/alteon/acenic.c
@@ -465,6 +465,7 @@ static int acenic_probe_one(struct pci_dev *pdev,
        SET_NETDEV_DEV(dev, &pdev->dev);

        ap = netdev_priv(dev);
+       ap->ndev = dev;
        ap->pdev = pdev;
        ap->name = pci_name(pdev);

@@ -1562,10 +1563,10 @@ static void ace_watchdog(struct net_device
*data, unsigned int txqueue)
 }


-static void ace_tasklet(unsigned long arg)
+static void ace_tasklet(struct tasklet_struct *t)
 {
-       struct net_device *dev = (struct net_device *) arg;
-       struct ace_private *ap = netdev_priv(dev);
+       struct ace_private *ap = from_tasklet(ap, t, ace_tasklet);
+       struct net_device *dev = ap->ndev;
        int cur_size;

        cur_size = atomic_read(&ap->cur_rx_bufs);
@@ -2269,7 +2270,7 @@ static int ace_open(struct net_device *dev)
        /*
         * Setup the bottom half rx ring refill handler
         */
-       tasklet_init(&ap->ace_tasklet, ace_tasklet, (unsigned long)dev);
+       tasklet_setup(&ap->ace_tasklet, ace_tasklet);
        return 0;
 }

diff --git a/drivers/net/ethernet/alteon/acenic.h
b/drivers/net/ethernet/alteon/acenic.h
index c670067b1541..265fa601a258 100644
--- a/drivers/net/ethernet/alteon/acenic.h
+++ b/drivers/net/ethernet/alteon/acenic.h
@@ -633,6 +633,7 @@ struct ace_skb
  */
 struct ace_private
 {
+       struct net_device       *ndev;          /* backpointer */
        struct ace_info         *info;
        struct ace_regs __iomem *regs;          /* register base */
        struct ace_skb          *skb;
@@ -776,7 +777,7 @@ static int ace_open(struct net_device *dev);
 static netdev_tx_t ace_start_xmit(struct sk_buff *skb,
                                  struct net_device *dev);
 static int ace_close(struct net_device *dev);
-static void ace_tasklet(unsigned long dev);
+static void ace_tasklet(struct tasklet_struct *t);
 static void ace_dump_trace(struct ace_private *ap);
 static void ace_set_multicast_list(struct net_device *dev);
 static int ace_change_mtu(struct net_device *dev, int new_mtu);

Let me know what you think.

Thanks.

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