Re: mmap()ed AF_NETLINK: lockdep and sleep-in-atomic warnings

[Thomas Graf <tgraf@suug.ch>]

On 07/13/15 at 10:11pm, Cong Wang wrote:
> Caused by:
> 
> commit 21e4902aea80ef35afc00ee8d2abdea4f519b7f7
> Author: Thomas Graf <tgraf@suug.ch>
> Date:   Fri Jan 2 23:00:22 2015 +0100
> 
>     netlink: Lockless lookup with RCU grace period in socket release
> 
>     Defers the release of the socket reference using call_rcu() to
>     allow using an RCU read-side protected call to rhashtable_lookup()
> 
>     This restores behaviour and performance gains as previously
>     introduced by e341694 ("netlink: Convert netlink_lookup() to use
>     RCU protected hash table") without the side effect of severely
>     delayed socket destruction.
> 
>     Signed-off-by: Thomas Graf <tgraf@suug.ch>
>     Signed-off-by: David S. Miller <davem@davemloft.net>
> 
> 
> We can't hold mutex lock in a rcu callback, perhaps we could
> defer the mmap ring cleanup to a workqueue.

The socket should be dead at this point. It might be simpler to
add a netlink_release_ring() function which doesn't require
locking at all. It would also get rid of all the special handling
for closing vs. non-closing.