linux-kernel - Re: [PATCH] RDMA/device: Fix a race between mad_client and cm

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Date: Fri, 5 Jan 2024 16:15:18 +0800
From: Shifeng Li <lishifeng@...gfor.com.cn>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: leon@...nel.org, wenglianfa@...wei.com, gustavoars@...nel.org,
 linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
 Shifeng Li <lishifeng1992@....com>, "Ding, Hui" <dinghui@...gfor.com.cn>
Subject: Re: [PATCH] RDMA/device: Fix a race between mad_client and cm_client
 init

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?

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

Thanks.

> You are trying to say that the post-client fixup stuff will still see
> the DEVICE_REGISTERED before it reaches the clients_rwsem lock?
> 
> That probably just says the clients_rwsem should be obtained before
> changing the DEVICE_STATE too :\
> 
> Jason
>