linux-kernel - Re: [PATCH 04/17] mm: pass the vmem_altmap to arch_add_memory and __add

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Date:   Fri, 22 Dec 2017 17:49:01 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jérôme Glisse <jglisse@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-nvdimm@...ts.01.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        X86 ML <x86@...nel.org>, Linux MM <linux-mm@...ck.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/17] mm: pass the vmem_altmap to arch_add_memory and __add_pages

On Fri, Dec 15, 2017 at 6:09 AM, Christoph Hellwig <hch@....de> wrote:
> We can just pass this on instead of having to do a radix tree lookup
> without proper locking 2 levels into the callchain.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
[..]
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 403ab9cdb949..16456117a1b1 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -427,7 +427,7 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
>                 goto err_pfn_remap;
>
>         mem_hotplug_begin();
> -       error = arch_add_memory(nid, align_start, align_size, false);
> +       error = arch_add_memory(nid, align_start, align_size, altmap, false);
>         if (!error)
>                 move_pfn_range_to_zone(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
>                                         align_start >> PAGE_SHIFT,

Subtle bug here. This altmap is the one that was passed in that we
copy into its permanent location in the pgmap, so it looks like this
patch needs to fold the following fix:

diff --git a/kernel/memremap.c b/kernel/memremap.c
index f277bf5b8c57..157a3756e1d5 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -382,6 +382,7 @@ void *devm_memremap_pages(struct device *dev,
struct resource *res,
        if (altmap) {
                memcpy(&page_map->altmap, altmap, sizeof(*altmap));
                pgmap->altmap = &page_map->altmap;
+               altmap = pgmap->altmap;
        }
        pgmap->ref = ref;
        pgmap->res = &page_map->res;