Re: [PATCH] Fix sendonly join going away after Reregister event

[Leon Romanovsky <leon@kernel.org>]

On Thu, Jan 21, 2021 at 01:24:43PM +0000, Christoph Lameter wrote:
> From: Christoph Lameter <cl@linux.com>
> Subject: [PATCH] Fix sendonly join going away after Reregister event
>
> When a server receives a REREG event then the SM information in
> the kernel is marked as invalid and a request is sent to the SM to update
> the information.
>
> However, receiving a REREG also occurs in user space applications that
> are now trying to rejoin the multicast groups.
>
> If the SM information is invalid then ib_sa_sendonly_fullmem_support()
> returns false. That is wrong because it just means that we do not know
> yet if the potentially new SM supports sendonly joins. It does not mean
> that the SM does not support Sendonly joins.
>
> This patch simply attempts to waits until the SM information is updated
> and the determination can be made.
>
> The code has not been testet but compiles fine.
> I am not sure if it is good to do an msleep here.
>
> Signed-off-by: Christoph Lameter <cl@linux.com>
>
> Index: linux/drivers/infiniband/core/sa_query.c
> ===================================================================
> --- linux.orig/drivers/infiniband/core/sa_query.c	2020-12-17 14:51:15.301206041 +0000
> +++ linux/drivers/infiniband/core/sa_query.c	2021-01-21 12:52:53.577943481 +0000
> @@ -1963,11 +1963,19 @@ bool ib_sa_sendonly_fullmem_support(stru
>  	if (!sa_dev)
>  		return ret;
>
> +redo:
>  	port  = &sa_dev->port[port_num - sa_dev->start_port];
>
> +	while (!port->classport_info.valid)
> +		msleep(100);
> +
>  	spin_lock_irqsave(&port->classport_lock, flags);
> -	if ((port->classport_info.valid) &&
> -	    (port->classport_info.data.type == RDMA_CLASS_PORT_INFO_IB))
> +	if (!port->classport_info.valid) {
> +		/* Need to wait until the SM data is available */
> +		spin_unlock_irqrestore(&port->classport_lock, flags);
> +		goto redo;

We have all potential to loop forever here, if valid doesn't change.

> +	}
> +	if ((port->classport_info.data.type == RDMA_CLASS_PORT_INFO_IB))
>  		ret = ib_get_cpi_capmask2(&port->classport_info.data.ib)
>  			& IB_SA_CAP_MASK2_SENDONLY_FULL_MEM_SUPPORT;
>  	spin_unlock_irqrestore(&port->classport_lock, flags);