Re: [PATCH rdma-next] IB/core: Avoid deadlock during netlink message handling

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Parav Pandit <parav@mellanox.com>
Cc: Leon Romanovsky <leon@kernel.org>,
	Doug Ledford <dledford@redhat.com>,
	RDMA mailing list <linux-rdma@vger.kernel.org>
Subject: Re: [PATCH rdma-next] IB/core: Avoid deadlock during netlink message handling
Date: Thu, 24 Oct 2019 20:53:04 -0300	[thread overview]
Message-ID: <20191024235304.GG23952@ziepe.ca> (raw)
In-Reply-To: <AM0PR05MB4866CA70E3711F8BE19F294ED16A0@AM0PR05MB4866.eurprd05.prod.outlook.com>

On Thu, Oct 24, 2019 at 07:53:56PM +0000, Parav Pandit wrote:

> Jason's memory size point made be curious about the srcu_struct
> size.  On my x86 5.x kernel I see srcu_struct costs 70+Kbytes!
> Likely due to some debug info in my kernel.  Which is probably a
> good reason in this case to shift to rwsem. (rwsem is 80 bytes).

Yikes, I knew it was bad, but I didn't think that bad.. So
unbelievable I checked here and I got +4752 bytes using SRCU on my
much less debug kernel. Crazy.

> One small comment correction needed is,
> 
> -	rdma_nl_types[index].cb_table = cb_table;
> -	mutex_unlock(&rdma_nl_mutex);
> +	/* Pairs with the READ_ONCE in is_nl_valid() */
> +	smp_store_release(&rdma_nl_types[index].cb_table, cb_table);
> 
> It should be "Pairs with the READ_ONE in get_cb_table() */

Done, applied to for-rc, thanks

Jason