netdev - Re: [PATCH v2 net 6/7] net/sched: taprio: fix q->current

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Date: Wed, 15 Nov 2023 19:56:35 +0800
From: "Abdul Rahim, Faizal" <faizal.abdul.rahim@...ux.intel.com>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: Vinicius Costa Gomes <vinicius.gomes@...el.com>,
 Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>,
 Jiri Pirko <jiri@...nulli.us>, "David S . Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net 6/7] net/sched: taprio: fix q->current_entry is
 NULL before its expiry



On 9/11/2023 7:55 pm, Vladimir Oltean wrote:
> On Tue, Nov 07, 2023 at 06:20:22AM -0500, Faizal Rahim wrote:
>> Fix the issue of prematurely setting q->current_entry to NULL in the
>> setup_first_end_time() function when a new admin schedule arrives
>> while the oper schedule is still running but hasn't transitioned yet.
>> This premature setting causes problems because any reference to
>> q->current_entry, such as in taprio_dequeue(), will result in NULL
>> during this period, which is incorrect. q->current_entry should remain
>> valid until the currently running entry expires.
>>
>> To address this issue, only set q->current_entry to NULL when there is
>> no oper schedule currently running.
>>
>> Fixes: 5a781ccbd19e ("tc: Add support for configuring the taprio scheduler")
> 
> The "Fixes" tag represents the commit where the code started becoming a
> problem, not when the code that you're changing was first introduced.
> 
> I find it hard to believe that the problem was in commit 5a781ccbd19e
> ("tc: Add support for configuring the taprio scheduler"), because we
> didn't support admin -> oper dynamic schedules back then.
> 

My bad, will update accordingly.

>> Signed-off-by: Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>
>> ---
>>   net/sched/sch_taprio.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
>> index 01b114edec30..c60e9e7ac193 100644
>> --- a/net/sched/sch_taprio.c
>> +++ b/net/sched/sch_taprio.c
>> @@ -1375,7 +1375,8 @@ static void setup_first_end_time(struct taprio_sched *q,
>>   			first->gate_close_time[tc] = ktime_add_ns(base, first->gate_duration[tc]);
>>   	}
>>   
>> -	rcu_assign_pointer(q->current_entry, NULL);
>> +	if (!hrtimer_active(&q->advance_timer))
>> +		rcu_assign_pointer(q->current_entry, NULL);
>>   }
>>   
>>   static void taprio_start_sched(struct Qdisc *sch,
>> -- 
>> 2.25.1
>>