Date:   Tue, 31 Jan 2023 19:56:29 +0900
From:   Hyunmin Lee <hn.min.lee@gmail.com>
To:     Mike Rapoport <rppt@kernel.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Uladzislau Rezki <urezki@gmail.com>,
        Christoph Hellwig <hch@infradead.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>,
        Jeungwoo Yoo <casionwoo@gmail.com>,
        Sangyun Kim <sangyun.kim@snu.ac.kr>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>
Subject: Re: [PATCH] replace BUG_ON to WARN_ON
Message-ID: <20230131105629.GA1195431@min-iamroot>
References: <20230127115844.GA1124261@min-iamroot>
 <Y9eYbPuq5Nw9Njxf@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y9eYbPuq5Nw9Njxf@kernel.org>
Precedence: bulk

On Mon, Jan 30, 2023 at 12:14:04PM +0200, Mike Rapoport wrote:
> Hi,
> 
> On Fri, Jan 27, 2023 at 08:58:44PM +0900, Hyunmin Lee wrote:
> > Replace unnacessary BUG_ON to WARN_ON. These BUG_ONs verify aruguments of a function. Thus, the WARN_ONs return an EINVAL error when their condition is true.
> 
> Some users enable panic_on_warn, so for them WARN_ON will still crash a
> machine.
> 
> I think a simple if() will be sufficient.
>  
> > Co-Developed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
> > Co-Developed-by: Jeungwoo Yoo <casionwoo@gmail.com>
> > Co-Developed-by: Sangyun Kim <sangyun.kim@snu.ac.kr>
> > Signed-off-by: Hyunmin Lee <hn.min.lee@gmail.com>
> > Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
> > Signed-off-by: Jeungwoo Yoo <casionwoo@gmail.com>
> > Signed-off-by: Sangyun Kim <sangyun.kim@snu.ac.kr>
> > Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> > ---
> >  mm/vmalloc.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 74afa2208558..9f9dba3132c5 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 (WARN_ON(!size))
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	if (WARN_ON(offset_in_page(size)))
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	if (WARN_ON(!is_power_of_2(align)))
> > +		return ERR_PTR(-EINVAL);
> >  
> >  	if (unlikely(!vmap_initialized))
> >  		return ERR_PTR(-EBUSY);
> > -- 
> > 2.25.1
> > 
> > 
> 
> -- 
> Sincerely yours,
> Mike.
Hi Mike,

Thank you for your advice.
Would you please give feedback about the below opinion?
- Printing warning messages is helpful to inform what happened in the system to the users.
- When a simple if() is used instead of WARN_ON, the if() should print a warning message.
- The condition of the simple if() should also have unlikely() for optimization of system performance.
- WARN_ON is a macro doing like thoes easily. It has a notifying function and unlikely optimization.
- Eventhough WARN_ON will still crash like BUG_ON by some users who enable panic_on_warn, it is their intention. They should accept the crash by WARN_ON.
- Therefore, using WARN_ON looks like natural and efficient.

Best,
Hyunmin