Re: [PATCH] Fix SMP support on 3c527 net driver

Manfred Spraul
2003-08-31T08:28:42Z

Felipe wrote:

>Also, the down/up function doesn't seem to be
>used in interrupt context, so I think it will work.
>
>
[snip]

> static int mc32_send_packet(struct sk_buff *skb, struct net_device *dev)
> {
> struct mc32_local *lp = (struct mc32_local *)dev->priv;
>- unsigned long flags;
>
> volatile struct skb_header *p, *np;
>
> netif_stop_queue(dev);
>
>- save_flags(flags);
>- cli();
>+ down(&lp->mc32_sem);
>
>
No, that's wrong. mc32_send_packet is the hard_start_xmit function,
called from bottom half context, with the dev_xmit_lock spinlock held.
Additionally, you must replace the sleep_on calls with wait_event, or an
open-coded wait queue: sleep_on is racy, it only works with cli().

IMHO the right way to fix cli() is
- add a single spinlock to the driver or the device structure. Do not
forget the spin_lock_init().
- replace cli/sti with spin_lock_irqsave/spin_unlock_irqsave.
- Additionally acquire the spinlock in every interrupt handler (cli()
stops all interrupts, spinlocks only stop interrupt on the current cpu).
- check if there were recursive cli() calls. Fix them.
- replace all sleep_on calls with wait queue calls.
- check if there are any kmalloc or schedule calls in the area now under
the spinlock, and reorganize the code.

And please add a changelog entry that code was converted without testing.

--
Manfred