linux-kernel - Re: [PATCH AUTOSEL 4.14 71/95] Revert "mm, memory_hotplug: initialize struct pages for the full memory section"

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Message-ID: <CAKgT0Uf89zkZDU5d5GO-i4B4igASXWqUioWCpoTsY92V4gEWjg@mail.gmail.com>
Date:   Tue, 7 May 2019 10:25:40 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>,
        Robert Shteynfeld <robert.shteynfeld@...il.com>,
        stable@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...rosoft.com>,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH AUTOSEL 4.14 71/95] Revert "mm, memory_hotplug: initialize
 struct pages for the full memory section"

On Mon, May 6, 2019 at 10:40 PM Sasha Levin <sashal@...nel.org> wrote:
>
> From: Michal Hocko <mhocko@...e.com>
>
> [ Upstream commit 4aa9fc2a435abe95a1e8d7f8c7b3d6356514b37a ]
>
> This reverts commit 2830bf6f05fb3e05bc4743274b806c821807a684.
>
> The underlying assumption that one sparse section belongs into a single
> numa node doesn't hold really. Robert Shteynfeld has reported a boot
> failure. The boot log was not captured but his memory layout is as
> follows:
>
>   Early memory node ranges
>     node   1: [mem 0x0000000000001000-0x0000000000090fff]
>     node   1: [mem 0x0000000000100000-0x00000000dbdf8fff]
>     node   1: [mem 0x0000000100000000-0x0000001423ffffff]
>     node   0: [mem 0x0000001424000000-0x0000002023ffffff]
>
> This means that node0 starts in the middle of a memory section which is
> also in node1.  memmap_init_zone tries to initialize padding of a
> section even when it is outside of the given pfn range because there are
> code paths (e.g.  memory hotplug) which assume that the full worth of
> memory section is always initialized.
>
> In this particular case, though, such a range is already intialized and
> most likely already managed by the page allocator.  Scribbling over
> those pages corrupts the internal state and likely blows up when any of
> those pages gets used.
>
> Reported-by: Robert Shteynfeld <robert.shteynfeld@...il.com>
> Fixes: 2830bf6f05fb ("mm, memory_hotplug: initialize struct pages for the full memory section")
> Cc: stable@...nel.org
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
> ---
>  mm/page_alloc.c | 12 ------------
>  1 file changed, 12 deletions(-)

So it looks like you already had the revert of the earlier patch I
pointed out enqueued as well. So you can probably at a minimum just
drop this patch and the earlier patch that this reverts.

Thanks.

- Alex