linux-kernel - Re: [PATCH v3] mm/vmalloc: replace BUG

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Date:   Wed, 1 Feb 2023 10:37:19 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Hyunmin Lee <hn.min.lee@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Christoph Hellwig <hch@...radead.org>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
        Jeungwoo Yoo <casionwoo@...il.com>,
        Sangyun Kim <sangyun.kim@....ac.kr>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH v3] mm/vmalloc: replace BUG_ON to a simple if statement



Le 01/02/2023 à 11:11, Hyunmin Lee a écrit :
> [Vous ne recevez pas souvent de courriers de hn.min.lee@...il.com. D?couvrez pourquoi ceci est important ? https://aka.ms/LearnAboutSenderIdentification ]
> 
> As per the coding standards, in the event of an abnormal condition that
> should not occur under normal circumstances, the kernel should attempt
> recovery and proceed with execution, rather than halting the machine.
> 
> Specifically, in the alloc_vmap_area() function, use a simple if()
> instead of using BUG_ON() halting the machine.
> 
> Co-Developed-by: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
> Co-Developed-by: Jeungwoo Yoo <casionwoo@...il.com>
> Co-Developed-by: Sangyun Kim <sangyun.kim@....ac.kr>
> Signed-off-by: Hyunmin Lee <hn.min.lee@...il.com>
> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
> Signed-off-by: Jeungwoo Yoo <casionwoo@...il.com>
> Signed-off-by: Sangyun Kim <sangyun.kim@....ac.kr>
> Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>
> ---
> v1->v2 : Add commit description
> v2->v3 : Change WARN_ON() to if()
> ---
>   mm/vmalloc.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 74afa2208558..52a346bc02a1 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1587,9 +1587,14 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>          int purged = 0;
>          int ret;
> 
> -       BUG_ON(!size);
> -       BUG_ON(offset_in_page(size));
> -       BUG_ON(!is_power_of_2(align));
> +       if (unlikely(!size))
> +               return ERR_PTR(-EINVAL);
> +
> +       if (unlikely(offset_in_page(size)))
> +               return ERR_PTR(-EINVAL);
> +
> +       if (unlikely(!is_power_of_2(align)))
> +               return ERR_PTR(-EINVAL);

I would have written it more compact. When using BUG_ON or WARN_ON it is 
interesting to have three separate lines because you get the line number 
in the Oops message, but here you are just returning the exact same 
error code, so it could be:

	if (unlikely(!size || offset_in_page(size) || !is_power_of_2(align)))
		return ERR_PTR(-EINVAL);

> 
>          if (unlikely(!vmap_initialized))
>                  return ERR_PTR(-EBUSY);
> --
> 2.25.1
> 
>