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

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Date: Wed, 31 Jan 2024 20:04:08 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Shifeng Li <lishifeng@...gfor.com.cn>
Cc: Ding Hui <dinghui@...gfor.com.cn>, leon@...nel.org,
	wenglianfa@...wei.com, gustavoars@...nel.org,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	Shifeng Li <lishifeng1992@....com>
Subject: Re: [PATCH] RDMA/device: Fix a race between mad_client and cm_client
 init

On Fri, Jan 26, 2024 at 10:25:01AM +0800, Shifeng Li wrote:
> > I believe this modification is effective, rather than expanding the clients_rwsem range,
> > the key point is down_write(&devices_rwsem), which prevents ib_register_client() from
> > being executed in the gap of ib_register_device().
> > 
> > However, this may cause a little confusion, as ib_register_client() does not modify
> > anything related to devices, but it is protected by a write lock.
> > 
> Do you have any differing opinions about above?

I'd rather see the client side have a comment explaining the confusing
lock then disturb the locking on the devices side..

I think the write/read lock scheme there was done for a reason I just
haven't had time to recall exactly why..

Please send a patch with this arrangement

Jason