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Date: Fri, 5 Jan 2024 10:19:44 -0400
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Shifeng Li <lishifeng@sangfor.com.cn>
Cc: leon@kernel.org, wenglianfa@huawei.com, gustavoars@kernel.org,
	linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
	Shifeng Li <lishifeng1992@126.com>,
	"Ding, Hui" <dinghui@sangfor.com.cn>
Subject: Re: [PATCH] RDMA/device: Fix a race between mad_client and cm_client
 init
Message-ID: <20240105141944.GF50608@ziepe.ca>
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In-Reply-To: <62db1a02-41b8-44b0-960b-6d6f5bec5d19@sangfor.com.cn>

On Fri, Jan 05, 2024 at 04:15:18PM +0800, Shifeng Li wrote:
> On 2024/1/4 20:37, Jason Gunthorpe wrote:
> > On Thu, Jan 04, 2024 at 02:48:14PM +0800, Shifeng Li wrote:
> > 
> > > The root cause is that mad_client and cm_client may init concurrently
> > > when devices_rwsem write semaphore is downgraded in enable_device_and_get() like:
> > 
> > That can't be true, the module loader infrastructue ensures those two
> > things are sequential.
> > 
> 
> I'm a bit confused how the module loader infrastructue ensures that mad_client.add() and
> cm_client.add() are sequential. Could you explain in more detail
> please?

ib_cm has a symbol dependency on ib_mad, so the module loader will not
allow ib_cm to start running until all its symbol dependencies have
completed loading.

> We know that the ib_cm driver and mlx5_ib driver can load concurrently.

Yes, this is possible

Jason