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Message-ID: <20e6c1dd-a195-4b49-8723-7c94f7562b4c@redhat.com>
Date:   Mon, 20 Nov 2023 09:56:18 +0100
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Subject: Re: [PATCH 1/3] mm/memory_hotplug: add missing mem_hotplug_lock
Content-Language: en-US
To:     Sumanth Korikkar <sumanthk@linux.ibm.com>,
        linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Oscar Salvador <osalvador@suse.de>, Michal Hocko <mhocko@suse.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        linux-s390 <linux-s390@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20231120072317.3169630-1-sumanthk@linux.ibm.com>
 <20231120072317.3169630-2-sumanthk@linux.ibm.com>
From:   David Hildenbrand <david@redhat.com>
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In-Reply-To: <20231120072317.3169630-2-sumanthk@linux.ibm.com>
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On 20.11.23 08:23, Sumanth Korikkar wrote:
>  From Documentation/core-api/memory-hotplug.rst:
> When adding/removing/onlining/offlining memory or adding/removing
> heterogeneous/device memory, we should always hold the mem_hotplug_lock
> in write mode to serialise memory hotplug (e.g. access to global/zone
> variables).
> 
> mhp_(de)init_memmap_on_memory() functions can change zone stats and
> struct page content, but they are currently called w/o the
> mem_hotplug_lock.
> 
> When memory block is being offlined and when kmemleak goes through each
> populated zone, the following theoretical race conditions could occur:
> CPU 0:					     | CPU 1:
> memory_offline()			     |
> -> offline_pages()			     |
> 	-> mem_hotplug_begin()		     |
> 	   ...				     |
> 	-> mem_hotplug_done()		     |
> 					     | kmemleak_scan()
> 					     | -> get_online_mems()
> 					     |    ...
> -> mhp_deinit_memmap_on_memory()	     |
>    [not protected by mem_hotplug_begin/done()]|
>    Marks memory section as offline,	     |   Retrieves zone_start_pfn
>    poisons vmemmap struct pages and updates   |   and struct page members.
>    the zone related data			     |
>     					     |    ...
>     					     | -> put_online_mems()
> 
> Fix this by ensuring mem_hotplug_lock is taken before performing
> mhp_init_memmap_on_memory(). Also ensure that
> mhp_deinit_memmap_on_memory() holds the lock.
> 
> online/offline_pages() are currently only called from
> memory_block_online/offline(), so it is safe to move the locking there.
> 
> Fixes: a08a2ae34613 ("mm,memory_hotplug: allocate memmap from the added memory range")
> Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
> Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb