linux-kernel - Re: [PATCH v2] net/core: Fix BUG to BUG

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Date:   Mon, 9 Oct 2017 16:06:20 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
Cc:     Tim Hansen <devtimhansen@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "willemb@...gle.com" <willemb@...gle.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "soheil@...gle.com" <soheil@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "elena.reshetova@...el.com" <elena.reshetova@...el.com>,
        "tom@...ntonium.net" <tom@...ntonium.net>,
        "Jason@...c4.com" <Jason@...c4.com>, "fw@...len.de" <fw@...len.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] net/core: Fix BUG to BUG_ON conditionals.

On Mon, Oct 09, 2017 at 08:26:34PM +0000, Levin, Alexander (Sasha Levin) wrote:
> On Mon, Oct 09, 2017 at 10:15:42AM -0700, Alexei Starovoitov wrote:
> >On Mon, Oct 09, 2017 at 11:37:59AM -0400, Tim Hansen wrote:
> >> Fix BUG() calls to use BUG_ON(conditional) macros.
> >>
> >> This was found using make coccicheck M=net/core on linux next
> >> tag next-2017092
> >>
> >> Signed-off-by: Tim Hansen <devtimhansen@...il.com>
> >> ---
> >>  net/core/skbuff.c | 15 ++++++---------
> >>  1 file changed, 6 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> >> index d98c2e3ce2bf..34ce4c1a0f3c 100644
> >> --- a/net/core/skbuff.c
> >> +++ b/net/core/skbuff.c
> >> @@ -1350,8 +1350,7 @@ struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
> >>  	/* Set the tail pointer and length */
> >>  	skb_put(n, skb->len);
> >>
> >> -	if (skb_copy_bits(skb, -headerlen, n->head, headerlen + skb->len))
> >> -		BUG();
> >> +	BUG_ON(skb_copy_bits(skb, -headerlen, n->head, headerlen + skb->len));
> >
> >I'm concerned with this change.
> >1. Calling non-trivial bit of code inside the macro is a poor coding style (imo)
> >2. BUG_ON != BUG. Some archs like mips and ppc have HAVE_ARCH_BUG_ON and implementation
> >of BUG and BUG_ON look quite different.
> 
> For these archs, wouldn't it then be more efficient to use BUG_ON rather than BUG()?

why more efficient? any data to prove that?
I'm pointing that the change is not equivalent and
this code has been around forever (pre-git days), so I see
no reason to risk changing it.