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SubjectRe: [PATCH net-next-2.6] bnx2: remove cancel_work_sync() from remove_one
Hello, David.

On Mon, Dec 20, 2010 at 01:11:46PM -0800, David Miller wrote:
> It would but we can't just make the change over to del_timer_sync()
> otherwise we'd deadlock on netif_tx_lock().
>
> But I think things might be OK as-is.
>
> The timer is deleted by dev_deactivate_many() which resets the qdisc
> to the no-op qdisc. Then it deletes the timer.
>
> Any running timer will complete or see the no-op qdisc attached and
> return immediately.
>
> synchronize_rcu() is then executed which guarentees completion.
>
> Since both the watchdog timer itself and the del_timer() call run
> with netif_tx_lock() held, this makes sure the timer, once deleted,
> will only see the no-op qdisc and return immediately if it is
> amidst running, else it has already returned when the timer delete
> completes.
>
> So we might be OK here.

Yeah, I agree the synchronize_rcu() there would guarantee the actual
timer completion but as it currently stands it looks a bit too subtle.
Maybe it's a good idea to add a big fat comment explaining that the
the timer is guaranteed to stop after close() and how it's guaranteed
through synchronize_rcu() at the moment? Also, it might be better to
use synchronize_sched() there as timer synchronization through
synchronize_rcu() is more of a happy accident.

Thanks.

--
tejun


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