linux-kernel - Re: [PATCH] rcu: tree_stall: Correctly unlock root node in rcu_check_gp_start

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Date:   Fri, 29 Mar 2019 19:52:15 +0530
From:   Neeraj Upadhyay <neeraju@...eaurora.org>
To:     Mukesh Ojha <mojha@...eaurora.org>, paulmck@...ux.vnet.ibm.com,
        josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        joel@...lfernandes.org
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: tree_stall: Correctly unlock root node in
 rcu_check_gp_start_stall



On 3/29/19 6:58 PM, Mukesh Ojha wrote:
> 
> On 3/29/2019 4:57 PM, Neeraj Upadhyay wrote:
>> Only unlock the root node, if current node (rnp) is not
>> root node.
>>
>> Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
> 
> 
> 
>> ---
>>   kernel/rcu/tree_stall.h | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
>> index f65a73a..0651833 100644
>> --- a/kernel/rcu/tree_stall.h
>> +++ b/kernel/rcu/tree_stall.h
> 
> 
> why this is showing as under tree_stall.h while it is under 
> "kernel/rcu/tree.c"

It's moved in 
https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=dev&id=10462d6f58fb6dbde7563e9343505d98d5bfba3d

Please see linux-rcu dev tree for other changes, which moves code to 
this file.


Thanks
Neeraj

> 
>> @@ -630,7 +630,9 @@ static void rcu_check_gp_start_stall(struct 
>> rcu_node *rnp, struct rcu_data *rdp,
>>           time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
>>           time_before(j, rcu_state.gp_activity + gpssdelay) ||
>>           atomic_xchg(&warned, 1)) {
>> -        raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */
>> +        if (rnp_root != rnp)
>> +            /* irqs remain disabled. */
>> +            raw_spin_unlock_rcu_node(rnp_root);
> 
> Looks good as it will balance the lock .if it is the root_node, which 
> was not there earlier, and unlock was happening without any lock on root.
> 
> Reviewed-by: Mukesh Ojha <mojha@...eaurora.org>
> 
> Cheers,
> -Mukesh
> 
>>           raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
>>           return;
>>       }

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