linux-kernel - Re: [PATCH] memblock: Add error message when memblock_can

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Message-ID: <20230614160710.GH52412@kernel.org>
Date:   Wed, 14 Jun 2023 19:07:10 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Song Shuai <songshuaishuai@...ylab.org>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memblock: Add error message when memblock_can_resize is
 not ready

Hi,

On Wed, Jun 14, 2023 at 09:17:46PM +0800, Song Shuai wrote:
> The memblock APIs are always correct, thus the callers usually don't
> handle the return code. But the failure caused by unready memblock_can_resize
> is hard to recognize without the return code. Like this piece of log:

Please make it clear that failure is in memblock_double_array(), e.g.

But when memblock_double_array() is called before memblock_can_resize
is true, it is hard to understand the actual reason for the failure.

> 
> ```
> [    0.000000] memblock_phys_alloc_range: 4096 bytes align=0x1000 from=0x0000000000000000 max_addr=0x0000000000000000 alloc_pmd_fixmap+0x14/0x1c
> [    0.000000] memblock_reserve: [0x000000017ffff000-0x000000017fffffff] memblock_alloc_range_nid+0xb8/0x128
> [    0.000000] Oops - store (or AMO) access fault [#1]
> ```
> 
> So add an error message for this kind of failure:
> 
> ```
> [    0.000000] memblock_phys_alloc_range: 4096 bytes align=0x1000 from=0x0000000000000000 max_addr=0x0000000000000000 alloc_pmd_fixmap+0x14/0x1c
> [    0.000000] memblock_reserve: [0x000000017ffff000-0x000000017fffffff] memblock_alloc_range_nid+0xb8/0x128
> [    0.000000] memblock: Can't double reserved array for area start 0x000000017ffff000 size 4096
> [    0.000000] Oops - store (or AMO) access fault [#1]
> ```
> 
> Signed-off-by: Song Shuai <songshuaishuai@...ylab.org>
> ---
>  mm/memblock.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 3feafea06ab2..ab952a164f62 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -418,8 +418,11 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
>  	/* We don't allow resizing until we know about the reserved regions
>  	 * of memory that aren't suitable for allocation
>  	 */
> -	if (!memblock_can_resize)
> +	if (!memblock_can_resize) {
> +		pr_err("memblock: Can't double %s array for area start %pa size %ld\n",
> +			type->name, &new_area_start, (unsigned long)new_area_size);

Most of the time memblock uses %llu and cast to u64 to print size, please
make this consistent.

>  		return -1;
> +	}
>  
>  	/* Calculate new doubled size */
>  	old_size = type->max * sizeof(struct memblock_region);
> -- 
> 2.20.1
> 
> 

-- 
Sincerely yours,
Mike.