linux-kernel - Re: [PATCH 11/12] device-dax: Add dis-contiguous resource support

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Date:   Tue, 12 May 2020 15:36:50 +0100
From:   Joao Martins <joao.m.martins@...cle.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-mm@...ck.org, vishal.l.verma@...el.com,
        dave.hansen@...ux.intel.com, hch@....de, linux-nvdimm@...ts.01.org,
        linux-kernel@...r.kernel.org, jmoyer@...hat.com
Subject: Re: [PATCH 11/12] device-dax: Add dis-contiguous resource support

On 3/23/20 11:55 PM, Dan Williams wrote:
> @@ -561,13 +580,26 @@ static int __alloc_dev_dax_range(struct dev_dax *dev_dax, u64 start,
>  	if (start == U64_MAX)
>  		return -EINVAL;
>  
> +	ranges = krealloc(dev_dax->ranges, sizeof(*ranges)
> +			* (dev_dax->nr_range + 1), GFP_KERNEL);
> +	if (!ranges)
> +		return -ENOMEM;
> +
>  	alloc = __request_region(res, start, size, dev_name(dev), 0);
> -	if (!alloc)
> +	if (!alloc) {
> +		kfree(ranges);
>  		return -ENOMEM;
> +	}

Noticed this yesterday while looking at alloc_dev_dax_range().

Is it correct to free @ranges here on __request_region failure?

IIUC krealloc() would free dev_dax->ranges if it succeeds, leaving us without
any valid ranges if __request_region failure case indeed frees @ranges. These
@ranges are being used afterwards when we delete the interface and free the
assigned regions. Perhaps we should remove the kfree() above and set
dev_dax->ranges instead before __request_region; or alternatively change the
call order between krealloc and __request_region? FWIW, krealloc checks if the
object being reallocated already meets the requested size, so perhaps there's no
harm with going with the former.

	Joao