linux-kernel - Re: [PATCH] dn_route: use time_is_before_jiffies(a) to replace "jiffies

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Date:   Fri, 29 Jul 2022 13:49:09 +0800
From:   Yu Zhe <yuzhe@...china.com>
To:     Paolo Abeni <pabeni@...hat.com>, davem@...emloft.net,
        kuba@...nel.org
Cc:     linux-decnet-user@...ts.sourceforge.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        liqiong@...china.com
Subject: Re: [PATCH] dn_route: use time_is_before_jiffies(a) to replace
 "jiffies - a > 0"

在 2022年07月28日 21:11, Paolo Abeni 写道:

> On Wed, 2022-07-27 at 10:46 +0800, Yu Zhe wrote:
>> time_is_before_jiffies deals with timer wrapping correctly.
>>
>> Signed-off-by: Yu Zhe <yuzhe@...china.com>
>> ---
>>   net/decnet/dn_route.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
>> index 552a53f1d5d0..0a4bed0bc2e3 100644
>> --- a/net/decnet/dn_route.c
>> +++ b/net/decnet/dn_route.c
>> @@ -201,7 +201,7 @@ static void dn_dst_check_expire(struct timer_list *unused)
>>   		}
>>   		spin_unlock(&dn_rt_hash_table[i].lock);
>>   
>> -		if ((jiffies - now) > 0)
>> +		if (time_is_before_jiffies(now))
> Uhmm... it looks like the wrap-around condition can happen only in
> theory: 'now' is initialized just before entering this loop, and we
> will break as soon as jiffies increment. The wrap-around could happen
> only if a single iteration of the loop takes more than LONG_MAX
> jiffies.
>
> If that happens, we have a completely different kind of much more
> serious problem, I think ;)
>
> So this change is mostly for core readability's sake. I personally find
> more readable:
>
> 		if (jiffies != now)

I agree and I will send a v2 patch later.

>
> Cheers,
>
> Paolo
>
> p.s. given the above I guess this is for the net-next tree, right?
>
yes

>