[openib-general] Re: ipoib_multicast_ah.patch
Michael S. Tsirkin
mst at mellanox.co.il
Mon Feb 27 00:59:24 PST 2006
Quoting r. Roland Dreier <rdreier at cisco.com>:
> Subject: Re: ipoib_multicast_ah.patch
>
> >> who else might change the value here? Answering this would
> >> help justify the patch and save me from having to write up a
> >> changelog entry.
>
> Michael> I has a quick look and couldnt see any other place -
> Michael> except when the mcast entry is freed. Am I missing
> Michael> something?
>
> I don't know if you're missing anything -- you posted the patch, and
> I'm just trying to understand the race it protects against. If
> nothing else could change the value in between the tests, then what's
> the harm in testing it twice?
I guess there's a misunderstanding here. Its pretty simple:
ipoib_mcast_send tests mcast->ah twice under priv->lock.
ipoib_mcast_join_finish modifies the mcast->ah without taking a lock.
No *other* place modifies the mcast->ah.
As a solution, take priv->lock around assignment to mcast->ah
thus making sure ipoib_mcast_send is not in flight.
OK?
--
Michael S. Tsirkin
Staff Engineer, Mellanox Technologies
More information about the general
mailing list