linux-kernel - Re: [PATCH] rdma_rxe: call comp_handler without holding cq->cq

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Message-ID: <e0f88ef5-b046-4128-8c81-ce3c7e20274c@linux.dev>
Date: Mon, 18 Aug 2025 19:37:16 -0700
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: Philipp Reisner <philipp.reisner@...bit.com>,
 Zhu Yanjun <zyjzyj2000@...il.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
 linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rdma_rxe: call comp_handler without holding cq->cq_lock

在 2025/8/6 5:39, Philipp Reisner 写道:
> Allow the comp_handler callback implementation to call ib_poll_cq().
> A call to ib_poll_cq() calls rxe_poll_cq() with the rdma_rxe driver.
> And rxe_poll_cq() locks cq->cq_lock. That leads to a spinlock deadlock.
> 
> The Mellanox and Intel drivers allow a comp_handler callback
> implementation to call ib_poll_cq().
> 
> Avoid the deadlock by calling the comp_handler callback without
> holding cq->cw_lock.
> 
> Signed-off-by: Philipp Reisner <philipp.reisner@...bit.com>
> ---
>   drivers/infiniband/sw/rxe/rxe_cq.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/infiniband/sw/rxe/rxe_cq.c b/drivers/infiniband/sw/rxe/rxe_cq.c
> index fffd144d509e..1195e109f89b 100644
> --- a/drivers/infiniband/sw/rxe/rxe_cq.c
> +++ b/drivers/infiniband/sw/rxe/rxe_cq.c
> @@ -88,6 +88,7 @@ int rxe_cq_post(struct rxe_cq *cq, struct rxe_cqe *cqe, int solicited)
>   	int full;
>   	void *addr;
>   	unsigned long flags;
> +	u8 notify;
>   
>   	spin_lock_irqsave(&cq->cq_lock, flags);
>   
> @@ -110,14 +111,15 @@ int rxe_cq_post(struct rxe_cq *cq, struct rxe_cqe *cqe, int solicited)
>   
>   	queue_advance_producer(cq->queue, QUEUE_TYPE_TO_CLIENT);
>   
> -	if ((cq->notify & IB_CQ_NEXT_COMP) ||
> -	    (cq->notify & IB_CQ_SOLICITED && solicited)) {
> -		cq->notify = 0;
> -		cq->ibcq.comp_handler(&cq->ibcq, cq->ibcq.cq_context);
> -	}
> +	notify = cq->notify;
> +	cq->notify = 0;

Thanks a lot. In the original source code, cq->notify is set to 0 in the 
following test cases:

if ((cq->notify & IB_CQ_NEXT_COMP) ||
	    (cq->notify & IB_CQ_SOLICITED && solicited))

but in your commit, the above test case is removed.
I am not sure if this will introduce any risk or not.

I am fine with others.

Reviewed-by: Zhu Yanjun <yanjun.zhu@...ux.dev>

Zhu Yanjun

>   
>   	spin_unlock_irqrestore(&cq->cq_lock, flags);
>   
> +	if ((notify & IB_CQ_NEXT_COMP) ||
> +	    (notify & IB_CQ_SOLICITED && solicited))
> +		cq->ibcq.comp_handler(&cq->ibcq, cq->ibcq.cq_context);
> +
>   	return 0;
>   }
>