Re: [PATCH 03/10] mac80211: Use rcu_barrier() on unload.

Johannes Berg
2009-06-23T15:15:55Z

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On Tue, 2009-06-23 at 17:04 +0200, Jesper Dangaard Brouer wrote:
> The mac80211 module uses rcu_call() thus it should use rcu_barrier()
> on module unload.
>
> I'm having a hardtime verifying that no more call_rcu() callbacks can
> be schedules in the module unload path. Could a maintainer please
> look into this?
>
> Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
> ---
>
> net/mac80211/main.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/net/mac80211/main.c b/net/mac80211/main.c
> index 092a017..e9f70ce 100644
> --- a/net/mac80211/main.c
> +++ b/net/mac80211/main.c
> @@ -1100,6 +1100,8 @@ static void __exit ieee80211_exit(void)
> ieee80211s_stop();
>
> ieee80211_debugfs_netdev_exit();
> +
> + rcu_barrier(); /* Wait for completion of call_rcu()'s */
> }

I don't think this is correct at all -- note that call_rcu() is done in
some of the mesh code, so I would think you need to do this in
ieee80211_stop() since the call_rcu() code requires the interface to
still be around. And when it's stopped everything should be idle.

I can fix it later, but I'm deep in some other stuff right now.

johannes

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