linux-kernel - Re: [PATCH 2/8] mm/memory_hotplug: fix error handling in add_memory

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Message-ID: <6c545504-e1a7-435b-aad9-b045247d6945@redhat.com>
Date:   Tue, 14 Nov 2023 19:36:20 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Sumanth Korikkar <sumanthk@...ux.ibm.com>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Oscar Salvador <osalvador@...e.de>, Michal Hocko <mhocko@...e.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vishal Verma <vishal.l.verma@...el.com>
Subject: Re: [PATCH 2/8] mm/memory_hotplug: fix error handling in
 add_memory_resource()

On 14.11.23 19:02, Sumanth Korikkar wrote:
> In add_memory_resource(), creation of memory block devices occurs after
> successful call to arch_add_memory(). However, creation of memory block
> devices could fail.  In that case, arch_remove_memory() is called to
> perform necessary cleanup.
> 
> Currently with or without altmap support, arch_remove_memory() is always
> passed with altmap set to NULL during error handling. This leads to
> freeing of struct pages using free_pages(), eventhough the allocation
> might have been performed with altmap support via
> altmap_alloc_block_buf().
> 
> Fix the error handling by passing altmap in arch_remove_memory(). This
> ensures the following:
> * When altmap is disabled, deallocation of the struct pages array occurs
>    via free_pages().
> * When altmap is enabled, deallocation occurs via vmem_altmap_free().
> 
> Fixes: db051a0dac13 ("mm/memory_hotplug: create memory block devices after arch_add_memory()")

That's the wrong commit. We didn't support memmap-on-memory back then.

Likely it should be:

Fixes: a08a2ae34613 ("mm,memory_hotplug: allocate memmap from the added 
memory range")

> Reviewed-by: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
> Signed-off-by: Sumanth Korikkar <sumanthk@...ux.ibm.com>
> ---
>   mm/memory_hotplug.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c8238fc5edcb..4f476a970e84 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1458,7 +1458,7 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
>   	/* create memory block devices after memory was added */
>   	ret = create_memory_block_devices(start, size, params.altmap, group);
>   	if (ret) {
> -		arch_remove_memory(start, size, NULL);
> +		arch_remove_memory(start, size, params.altmap);
>   		goto error_free;
>   	}
>   

Indeed; this will conflict with Vishals patches, ccing him.

-- 
Cheers,

David / dhildenb