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

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Date:   Wed, 1 Feb 2023 20:41:34 +0900
From:   Hyunmin Lee <hn.min.lee@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Christoph Hellwig <hch@...radead.org>, linux-mm@...ck.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>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>
Subject: Re: [PATCH v3] mm/vmalloc: replace BUG_ON to a simple if statement

On Wed, Feb 01, 2023 at 10:37:19AM +0000, Christophe Leroy wrote:
> 
> 
> 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
> > 
> > 
Hi Christophe,

Thanks for your comment.
I will send new patch.

Best,
Min