linux-kernel - Re: [PATCH] neighbour: Convert if statment in the function, neigh_add_timer to a WARN

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Date:	Mon, 1 Jun 2015 20:37:21 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	YOSHIFUJI Hideaki/吉藤英明 
	<hideaki.yoshifuji@...aclelinux.com>
Cc:	Nicholas Krause <xerofoify@...il.com>,
	David Miller <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	johannes.berg@...el.com,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] neighbour: Convert if statment in the function,
 neigh_add_timer to a WARN_ON

On Mon, Jun 1, 2015 at 7:37 PM, YOSHIFUJI Hideaki/吉藤英明
<hideaki.yoshifuji@...aclelinux.com> wrote:
> Nicholas Krause wrote:
>> This converts the if statement for dumping the stack into a
>> WARN_ON in order to make this function's debugging check
>> simpler and have a cleaner output when this condition
>> occurs inside this function for when bugs related to
>> adding a duplicate neighbour table timer arise.
>>
>> Signed-off-by: Nicholas Krause <xerofoify@...il.com>
>> ---
>>  net/core/neighbour.c | 6 +-----
>>  1 file changed, 1 insertion(+), 5 deletions(-)
>>
>> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
>> index 3de6542..0bf71da 100644
>> --- a/net/core/neighbour.c
>> +++ b/net/core/neighbour.c
>> @@ -165,11 +165,7 @@ static int neigh_forced_gc(struct neigh_table *tbl)
>>  static void neigh_add_timer(struct neighbour *n, unsigned long when)
>>  {
>>       neigh_hold(n);
>> -     if (unlikely(mod_timer(&n->timer, when))) {
>> -             printk("NEIGH: BUG, double timer add, state is %x\n",
>> -                    n->nud_state);
>> -             dump_stack();
>> -     }
>> +     WARN_ON(unlikely(mod_timer(&n->timer, when)));
>>  }
>
> NACK, please do not use WARN_ON for things with side effects.

Just:

int ret = mod_timer(...);
WARN_ON(ret);
...
--
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