linux-kernel - Re: [PATCH] LoongArch: Set all reserved memblocks on Node#0 at initialization

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Message-ID: <b96c53eb-3c6f-d981-7573-10b95c3005a2@xen0n.name>
Date:   Wed, 13 Sep 2023 00:07:51 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     Huacai Chen <chenhuacai@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     loongarch@...ts.linux.dev, Xuefeng Li <lixuefeng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn,
        WANG Xuerui <git@...0n.name>
Subject: Re: [PATCH] LoongArch: Set all reserved memblocks on Node#0 at
 initialization

On 9/11/23 17:28, Huacai Chen wrote:
> After commit 61167ad5fecdea ("mm: pass nid to reserve_bootmem_region()")
> we get a panic if DEFERRED_STRUCT_PAGE_INIT is enabled:
>
> [snip]
>
> The reason is early memblock_reserve() in memblock_init() set node id
Why is it that only "early" but not "late" memblock_reserve() matters? I 
failed to see the reason because the arch-specific memblock_init() isn't 
even in the backtrace, which means that *neither* is the culprit.
> to MAX_NUMNODES, which causes NODE_DATA(nid) be a NULL dereference in
"making NODE_DATA(nid) a NULL ..."
> reserve_bootmem_region() -> init_reserved_page(). So set all reserved
> memblocks on Node#0 at initialization to avoid this panic.
>
> Reported-by: WANG Xuerui <git@...0n.name>
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
>   arch/loongarch/kernel/mem.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/kernel/mem.c b/arch/loongarch/kernel/mem.c
> index 4a4107a6a965..aed901c57fb4 100644
> --- a/arch/loongarch/kernel/mem.c
> +++ b/arch/loongarch/kernel/mem.c
> @@ -50,7 +50,6 @@ void __init memblock_init(void)
>   	}
>   
>   	memblock_set_current_limit(PFN_PHYS(max_low_pfn));
> -	memblock_set_node(0, PHYS_ADDR_MAX, &memblock.memory, 0);
>   
>   	/* Reserve the first 2MB */
>   	memblock_reserve(PHYS_OFFSET, 0x200000);
> @@ -58,4 +57,7 @@ void __init memblock_init(void)
>   	/* Reserve the kernel text/data/bss */
>   	memblock_reserve(__pa_symbol(&_text),
>   			 __pa_symbol(&_end) - __pa_symbol(&_text));
> +
> +	memblock_set_node(0, PHYS_ADDR_MAX, &memblock.memory, 0);
> +	memblock_set_node(0, PHYS_ADDR_MAX, &memblock.reserved, 0);
So the reordering is for being able to override the newly added 
memblocks' nids to 0, and additionally doing the same for 
memblock.reserved is the actual fix. Looks okay.
>   }

And I've tested the patch on the 2-way 3C5000L server, and it now 
correctly boots with deferred struct page init enabled. Thanks for 
providing such a quick fix!

Tested-by: WANG Xuerui <git@...0n.name>
Reviewed-by: WANG Xuerui <git@...0n.name>  # with nits addressed

-- 
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/