Re: [PATCH] rds: rds_ib_device.refcount overflow

[Wengang Wang <wen.gang.wang-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

Hi Doug,

How do you think about this patch?

thanks,
wengang

在 2015年07月06日 14:35, Wengang Wang 写道:
> Fixes: 3e0249f9c05c ("RDS/IB: add refcount tracking to struct rds_ib_device")
>
> There lacks a dropping on rds_ib_device.refcount in case rds_ib_alloc_fmr
> failed(mr pool running out). this lead to the refcount overflow.
>
> A complain in line 117(see following) is seen. From vmcore:
> s_ib_rdma_mr_pool_depleted is 2147485544 and rds_ibdev->refcount is -2147475448.
> That is the evidence the mr pool is used up. so rds_ib_alloc_fmr is very likely
> to return ERR_PTR(-EAGAIN).
>
> 115 void rds_ib_dev_put(struct rds_ib_device *rds_ibdev)
> 116 {
> 117         BUG_ON(atomic_read(&rds_ibdev->refcount) <= 0);
> 118         if (atomic_dec_and_test(&rds_ibdev->refcount))
> 119                 queue_work(rds_wq, &rds_ibdev->free_work);
> 120 }
>
> fix is to drop refcount when rds_ib_alloc_fmr failed.
>
> Signed-off-by: Wengang Wang <wen.gang.wang-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> Reviewed-by: Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> ---
>   net/rds/ib_rdma.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/rds/ib_rdma.c b/net/rds/ib_rdma.c
> index 273b8bf..657ba9f 100644
> --- a/net/rds/ib_rdma.c
> +++ b/net/rds/ib_rdma.c
> @@ -759,8 +759,10 @@ void *rds_ib_get_mr(struct scatterlist *sg, unsigned long nents,
>   	}
>   
>   	ibmr = rds_ib_alloc_fmr(rds_ibdev);
> -	if (IS_ERR(ibmr))
> +	if (IS_ERR(ibmr)) {
> +		rds_ib_dev_put(rds_ibdev);
>   		return ibmr;
> +	}
>   
>   	ret = rds_ib_map_fmr(rds_ibdev, ibmr, sg, nents);
>   	if (ret == 0)

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