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In-Reply-To: <20171215140947.26075-15-hch@lst.de>
References: <20171215140947.26075-1-hch@lst.de> <20171215140947.26075-15-hch@lst.de>
From: Dan Williams <dan.j.williams@intel.com>
Date: Sun, 17 Dec 2017 09:34:11 -0800
Message-ID: <CAPcyv4i2naLJjWzm+q0ORRfyHkT0f5dFBFKutuaXE3OgPcHX5g@mail.gmail.com>
Subject: Re: [PATCH 14/17] memremap: simplify duplicate region handling in devm_memremap_pages
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Sender: owner-linux-mm@kvack.org
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To: Christoph Hellwig <hch@lst.de>
Cc: =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>, Logan Gunthorpe <logang@deltatee.com>, "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, X86 ML <x86@kernel.org>, Linux MM <linux-mm@kvack.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>

On Fri, Dec 15, 2017 at 6:09 AM, Christoph Hellwig <hch@lst.de> wrote:
> __radix_tree_insert already checks for duplicates and returns -EEXIST in
> that case, so remove the duplicate (and racy) duplicates check.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
> ---
>  kernel/memremap.c | 11 -----------
>  1 file changed, 11 deletions(-)
>
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 891491ddccdb..901404094df1 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -395,17 +395,6 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
>         align_end = align_start + align_size - 1;
>
>         foreach_order_pgoff(res, order, pgoff) {
> -               struct dev_pagemap *dup;
> -
> -               rcu_read_lock();
> -               dup = find_dev_pagemap(res->start + PFN_PHYS(pgoff));
> -               rcu_read_unlock();
> -               if (dup) {
> -                       dev_err(dev, "%s: %pr collides with mapping for %s\n",
> -                                       __func__, res, dev_name(dup->dev));
> -                       error = -EBUSY;
> -                       break;
> -               }
>                 error = __radix_tree_insert(&pgmap_radix,
>                                 PHYS_PFN(res->start) + pgoff, order, page_map);
>                 if (error) {


This is not racy, we'll catch the error on insert, and I think the
extra debug information is useful for debugging a broken memory map or
alignment math.

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