Re: [PATCH] mm/percpu.c: Modify calculation of size of populated bitmap of chunk for memory allocation

[Vlastimil Babka <vbabka@suse.cz>]

On 9/3/20 2:41 PM, mcsmonk wrote:
> From: Sunghyun Jin <mcsmonk@gmail.com>
> 
> Variable populated, which is a member of struct pcpu_chunk, is used as a
> unit of size of unsigned long.
> However, size of populated is miscounted. So, I fix this minor part.

+CC folks who touched it last

Nice find! Did you observe e.g. a panic that can be used in the commit log? Or
were we always lucky thanks to alignment?
Is there perhaps a commit that introduced the bug and we can use it as Fixes:?
My brief look suggests 8ab16c43ea79 ("percpu: change the number of pages marked
in the first_chunk pop bitmap")

Thanks!

> Signed-off-by: Sunghyun Jin <mcsmonk@gmail.com>
> ---
>  mm/percpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/percpu.c b/mm/percpu.c
> index f4709629e6de..1ed1a349eab8 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -1316,7 +1316,7 @@ static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,
>  
>  	/* allocate chunk */
>  	alloc_size = sizeof(struct pcpu_chunk) +
> -		BITS_TO_LONGS(region_size >> PAGE_SHIFT);
> +		BITS_TO_LONGS(region_size >> PAGE_SHIFT) * sizeof(unsigned long);
>  	chunk = memblock_alloc(alloc_size, SMP_CACHE_BYTES);
>  	if (!chunk)
>  		panic("%s: Failed to allocate %zu bytes\n", __func__,
>