linux-kernel - Re: [PATCH] ipmi: fix suspicious RCU usage warning

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Message-ID: <e28d914d-5842-4bfa-8208-9ac34fd38a95@paulmck-laptop>
Date: Wed, 12 Mar 2025 10:29:10 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Rik van Riel <riel@...riel.com>
Cc: Corey Minyard <corey@...yard.net>,
	openipmi-developer@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH] ipmi: fix suspicious RCU usage warning

On Wed, Mar 12, 2025 at 01:19:32PM -0400, Rik van Riel wrote:
> On recent kernels this warning fires:
> 
> drivers/char/ipmi/ipmi_msghandler.c:1238 RCU-list traversed in non-reader section!!
> 
> This looks like a fairly simple lockdep trigger, where
> list_for_each_entry_rcu and list_for_each_entry_srcu are
> functionally identical, but the lockdep annotation in
> the former has an extra check.
> 
> That extra check is whether the RCU read lock is held,
> which is not true when the code uses srcu_read_lock.
> 
> Get rid of the warning by using the properly annotated
> list traversal macro.
> 
> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  drivers/char/ipmi/ipmi_msghandler.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index 1e5313748f8b..a2823763fd37 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -1235,7 +1235,7 @@ int ipmi_create_user(unsigned int          if_num,
>  		return -ENOMEM;
>  
>  	index = srcu_read_lock(&ipmi_interfaces_srcu);
> -	list_for_each_entry_rcu(intf, &ipmi_interfaces, link) {
> +	list_for_each_entry_srcu(intf, &ipmi_interfaces, link) {

Doesn't the above line want to be something like this?

+	list_for_each_entry_srcu(intf, &ipmi_interfaces, link,
				 srcu_read_lock_held(&ipmi_interfaces_srcu)) {

>  		if (intf->intf_num == if_num)
>  			goto found;
>  	}
> -- 
> 2.48.1
>