linux-kernel - Re: [PATCH v1] drivers/base/memory.c: Don't access uninitialized memmaps in soft_offline_page

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Date:   Fri, 11 Oct 2019 15:16:34 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Subject: Re: [PATCH v1] drivers/base/memory.c: Don't access uninitialized
 memmaps in soft_offline_page_store()

On Thu, 10 Oct 2019 16:12:00 +0200 David Hildenbrand <david@...hat.com> wrote:

> Uninitialized memmaps contain garbage and in the worst case trigger kernel
> BUGs, especially with CONFIG_PAGE_POISONING. They should not get
> touched.
> 
> Right now, when trying to soft-offline a PFN that resides on a memory
> block that was never onlined, one gets a misleading error with
> CONFIG_PAGE_POISONING:
>   :/# echo 5637144576 > /sys/devices/system/memory/soft_offline_page
>   [   23.097167] soft offline: 0x150000 page already poisoned
> 
> But the actual result depends on the garbage in the memmap.
> 
> soft_offline_page() can only work with online pages, it returns -EIO in
> case of ZONE_DEVICE. Make sure to only forward pages that are online
> (iow, managed by the buddy) and, therefore, have an initialized memmap.
> 
> Add a check against pfn_to_online_page() and similarly return -EIO.
> 
> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319

Should this be cc:stable?

What is the relationship between this and some similar fixes in the
series "mm/memory_hotplug: Shrink zones before removing memory", v6?

Should any of the patches in "mm/memory_hotplug: Shrink zones before
removing memory", v6 be cc:stable?