linux-kernel - Re: [PATCH] replace BUG_ON to WARN

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Message-ID: <Y9kb2XUunZlgsu2z@kernel.org>
Date:   Tue, 31 Jan 2023 15:47:05 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Hyunmin Lee <hn.min.lee@...il.com>
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] replace BUG_ON to WARN_ON

On Tue, Jan 31, 2023 at 07:56:29PM +0900, Hyunmin Lee wrote:
> 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.
> >  
> 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.

As this is a validation of the function parameters, there is no need in
warning messages and if(unlikely()) will do. There is really no point in
WARN_ON() for something that's totally recoverable and very unlikely to
happen.
 
> Best,
> Hyunmin

-- 
Sincerely yours,
Mike.