linux-kernel - Re: [PATCH v2] sh: Call paging_init() earlier in the init sequence

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Date: Thu, 02 May 2024 12:29:47 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: Oreoluwa Babatunde <quic_obabatun@...cinc.com>, 
	ysato@...rs.sourceforge.jp, dalias@...c.org
Cc: akpm@...ux-foundation.org, linux-sh@...r.kernel.org, 
 linux-kernel@...r.kernel.org, robh+dt@...nel.org, kernel@...cinc.com, Rob
 Herring <robh@...nel.org>, Rob Landley <rob@...dley.net>
Subject: Re: [PATCH v2] sh: Call paging_init() earlier in the init sequence

Hi Oreoluwa,

On Wed, 2024-05-01 at 19:18 +0200, John Paul Adrian Glaubitz wrote:
> Hi Oreoluwa,
> 
> On Tue, 2024-04-23 at 16:31 -0700, Oreoluwa Babatunde wrote:
> > The unflatten_device_tree() function contains a call to
> > memblock_alloc(). This is a problem because this allocation is done
> > before any of the reserved memory is set aside in paging_init().
> > This means that there is a possibility for memblock to allocate from
> > any of the memory regions that are supposed to be set aside as reserved.
> > 
> > Hence, move the call to paging_init() to be earlier in the init
> > sequence so that the reserved memory regions are set aside before any
> > allocations are done using memblock.
> 
> I was just about to merge your patch when I ran a git blame on the code in
> arch/sh/kernel/setup.c and noticed the following commit by Rich Felker:
> 
> commit eb6b6930a70faefe04479a71088cc10366782d9a
> Author: Rich Felker <dalias@...c.org>
> Date:   Mon Jul 31 01:27:50 2017 -0400
> 
>     sh: fix memory corruption of unflattened device tree
>     
>     unflatten_device_tree() makes use of memblock allocation, and
>     therefore must be called before paging_init() migrates the memblock
>     allocation data to the bootmem framework. Otherwise the record of the
>     allocation for the expanded device tree will be lost, and will
>     eventually be clobbered when allocated for another use.
>     
>     Signed-off-by: Rich Felker <dalias@...c.org>
> 
> It looks like that the call to unflatten_device_tree() before paging_init()
> is intentional and needed for the device tree to be preserved in memory
> after running paging_init().
> 
> @Geert: Do you have any comments on this patch?
> @Rob: Could you test this patch on your J2 board and report back?

I'm skipping this patch for v6.10 now for the aforementioned reasons.

Adrian

-- 
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