linux-kernel - Re: [PATCH v3] m68k: Fix memblock-related crashes

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Date:   Wed, 12 Dec 2018 15:58:42 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Andreas Schwab <schwab@...ux-m68k.org>, rppt@...ux.ibm.com,
        Michael Schmitz <schmitzmic@...il.com>
Cc:     Sam Creasey <sammy@...my.net>, Greg Ungerer <gerg@...ux-m68k.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] m68k: Fix memblock-related crashes

Hi Andreas,

On Fri, Dec 7, 2018 at 5:50 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> When running the kernel in Fast RAM on Atari:
>
>     Ignoring memory chunk at 0x0:0xe00000 before the first chunk
>     ...
>     Unable to handle kernel NULL pointer dereference at virtual address (ptrval)
>     Oops: 00000000
>     Modules linked in:
>     PC: [<0069dbac>] free_all_bootmem+0x12c/0x186
>     SR: 2714  SP: (ptrval)  a2: 005e3314
>     d0: 00000000    d1: 0000000a    d2: 00000e00    d3: 00000000
>     d4: 005e1fc0    d5: 0000001a    a0: 01000000    a1: 00000000
>     Process swapper (pid: 0, task=(ptrval))
>     Frame format=7 eff addr=00000736 ssw=0505 faddr=00000736
>     wb 1 stat/addr/data: 0000 00000000 00000000
>     wb 2 stat/addr/data: 0000 00000000 00000000
>     wb 3 stat/addr/data: 0000 00000736 00000000
>     push data: 00000000 00000000 00000000 00000000
>     Stack from 005e1f84:
>             00000000 0000000a 027d3260 006b5006 00000000 00000000 00000000 00000000
>             0004f062 0003a220 0069e272 005e1ff8 0000054c 00000000 00e00000 00000000
>             00000001 00693cd8 027d3260 0004f062 0003a220 00691be6 00000000 00000000
>             00000000 00000000 00000000 00000000 006b5006 00000000 00690872
>     Call Trace: [<0004f062>] printk+0x0/0x18
>      [<0003a220>] parse_args+0x0/0x2d4
>      [<0069e272>] memblock_virt_alloc_try_nid+0x0/0xa4
>      [<00693cd8>] mem_init+0xa/0x5c
>      [<0004f062>] printk+0x0/0x18
>      [<0003a220>] parse_args+0x0/0x2d4
>      [<00691be6>] start_kernel+0x1ca/0x462
>      [<00690872>] _sinittext+0x872/0x11f8
>     Code: 7a1a eaae 2270 6db0 0061 ef14 2f01 2f03 <96a9> 0736 2203 e589 d681 e78b d6a9 0732 2f03 2f40 0034 4eb9 0069 b8d0 260e 4fef
>     Disabling lock debugging due to kernel taint
>     Kernel panic - not syncing: Attempted to kill the idle task!
>
> As the kernel must run in the memory chunk with the lowest address,
> ST-RAM is ignored, and removed from the m68k_memory[] array.
> However, it is not removed from memblock, causing a crash later.
>
> More investigation shows that there are 3 places where memory chunks are
> ignored, all after the calls to memblock_add() in m68k_parse_bootinfo(),
> and thus causing crashes:
>   1. On classic m68k CPUs with a MMU, paging_init() ignores all memory
>      chunks below the first chunk, cfr. above,
>   2. On Amigas equipped with a Zorro III bus, config_amiga() ignores all
>      Zorro II memory,
>   3. If CONFIG_SINGLE_MEMORY_CHUNK=y, m68k_parse_bootinfo() ignores all
>      but the first memory chunk.
>
> Fix this by moving the calls to memblock_add() from
> m68k_parse_bootinfo() to paging_init(), after all ignored memory chunks
> have been removed from m68k_memory[].
>
> Reported-by: Andreas Schwab <schwab@...ux-m68k.org>
> Fixes: 1008a11590b966b4 ("m68k: switch to MEMBLOCK + NO_BOOTMEM")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Does this patch fix your crash?

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds