linux-kernel - Re: [PATCH 3/3] rcu: Report callbacks enqueued on offline CPU blind spot

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Message-ID: <a48ec24f-fe53-4a62-9397-e42a23fc3a2d@amd.com>
Date: Wed, 9 Oct 2024 07:54:15 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: Frederic Weisbecker <frederic@...nel.org>,
 LKML <linux-kernel@...r.kernel.org>
Cc: Boqun Feng <boqun.feng@...il.com>, Joel Fernandes
 <joel@...lfernandes.org>, "Paul E . McKenney" <paulmck@...nel.org>,
 Uladzislau Rezki <urezki@...il.com>, Zqiang <qiang.zhang1211@...il.com>,
 rcu <rcu@...r.kernel.org>
Subject: Re: [PATCH 3/3] rcu: Report callbacks enqueued on offline CPU blind
 spot

On 10/2/2024 8:30 PM, Frederic Weisbecker wrote:
> Le Wed, Oct 02, 2024 at 04:57:38PM +0200, Frederic Weisbecker a écrit :
>> Callbacks enqueued after rcutree_report_cpu_dead() fall into RCU barrier
>> blind spot. Report any potential misuse.
>>
>> Reported-by: Paul E. McKenney <paulmck@...nel.org>
>> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
>> ---
>>  kernel/rcu/tree.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>> index a60616e69b66..36070b6bf4a1 100644
>> --- a/kernel/rcu/tree.c
>> +++ b/kernel/rcu/tree.c
>> @@ -3084,8 +3084,11 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
>>  	head->func = func;
>>  	head->next = NULL;
>>  	kasan_record_aux_stack_noalloc(head);
>> +
>>  	local_irq_save(flags);
>>  	rdp = this_cpu_ptr(&rcu_data);
>> +	RCU_LOCKDEP_WARN(rcu_rdp_cpu_online(rdp), "Callback enqueued on offline
>> CPU!");
> 
> This should be !rcu_rdp_cpu_online(rdp)
> 

With this patch series, 600 mins RCU torture overnight testing completed
without failures at my end.

- Neeraj

> Sigh...
> 
>> +
>>  	lazy = lazy_in && !rcu_async_should_hurry();
>>  
>>  	/* Add the callback to our list. */
>> -- 
>> 2.46.0
>>
>>