Messages in this thread | | | Date | Sun, 12 Feb 2006 18:56:57 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [openib-general] Re: [git patch review 1/4] IPoIB: Don't start send-only joins while multicast thread is stopped |
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Quoting r. Roland Dreier <rdreier@cisco.com>: > Subject: Re: [openib-general] Re: [git patch review 1/4] IPoIB: Don't start send-only joins while multicast thread is stopped > > Michael> Basically, its as Andrew said: the lock around clear_bit > Michael> is there to ensure that ipoib_mcast_send isnt running > Michael> already when we stop the thread. Thats why test_bit has > Michael> to be inside the lock, too. > > Makes sense I guess. If I'm understanding correctly, the lock isn't > really there to serialize the bit ops, but rather to make sure > ipoib_mcast_send() won't do anything after we clear the bit.
Right. Thats one way to put it.
> Does that mean that there's no reason to take the lock around the set_bit()?
Ugh, sorry, I dont really remember why I put it there.
I guess I just have easier time reasoning about locks than barriers and atomic operations. "bit is protected by priv->lock" is a simple rule, and we are not on data path here. The fact that the race went unnoticed for a while validates this approach in my eyes.
I guess longer term we will replace mcast_mutex with priv->lock anyway, so it doesnt matter much.
-- Michael S. Tsirkin Staff Engineer, Mellanox Technologies - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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