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Subject: Re: [PATCH] nvme-rdma: handle nvme completion data length
To:     zhenwei pi <pizhenwei@bytedance.com>, <kbusch@kernel.org>,
        <hch@lst.de>, <sagi@grimberg.me>, <axboe@fb.com>
CC:     <linux-kernel@vger.kernel.org>, <linux-nvme@lists.infradead.org>
References: <20201022083850.1334880-1-pizhenwei@bytedance.com>
From:   Chao Leng <lengchao@huawei.com>
Message-ID: <04a97f73-ba13-a4b5-3ea4-fc438391507e@huawei.com>
Date:   Thu, 22 Oct 2020 17:55:01 +0800
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On 2020/10/22 16:38, zhenwei pi wrote:
> Hit a kernel warning:
> refcount_t: underflow; use-after-free.
> WARNING: CPU: 0 PID: 0 at lib/refcount.c:28
> 
> RIP: 0010:refcount_warn_saturate+0xd9/0xe0
> Call Trace:
>   <IRQ>
>   nvme_rdma_recv_done+0xf3/0x280 [nvme_rdma]
>   __ib_process_cq+0x76/0x150 [ib_core]
>   ...
> 
> The reason is that a zero bytes message received from target, and the
> host side continues to process without length checking, then the
> previous CQE is processed twice.
> 
> Handle data length, ignore zero bytes message, and try to recovery for
> corrupted CQE case.
> 
> Signed-off-by: zhenwei pi <pizhenwei@bytedance.com>
> ---
>   drivers/nvme/host/rdma.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
> index 9e378d0a0c01..9f5112040d43 100644
> --- a/drivers/nvme/host/rdma.c
> +++ b/drivers/nvme/host/rdma.c
> @@ -1767,6 +1767,17 @@ static void nvme_rdma_recv_done(struct ib_cq *cq, struct ib_wc *wc)
>   		return;
>   	}
>   
> +	if (unlikely(!wc->byte_len)) {
> +		/* zero bytes message could be ignored */
> +		return;
> +	} else if (unlikely(wc->byte_len < len)) {
> +		/* Corrupted completion, try to recovry */
> +		dev_err(queue->ctrl->ctrl.device,
> +			"Unexpected nvme completion length(%d)\n", wc->byte_len);
> +		nvme_rdma_error_recovery(queue->ctrl);
> +		return;
> +	}
!wc->byte_len and wc->byte_len < len may be the same type of anomaly.
Why do different error handling?
In which scenario zero bytes message received from target? fault inject test or normal test/run?
> +
>   	ib_dma_sync_single_for_cpu(ibdev, qe->dma, len, DMA_FROM_DEVICE);
>   	/*
>   	 * AEN requests are special as they don't time out and can
>