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

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Message-ID: <72ec7831604326e852eb228072b1d817bab829fb.camel@physik.fu-berlin.de>
Date: Wed, 01 May 2024 19:18:21 +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 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?

Thanks,
Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer
`. `'   Physicist
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