linux-kernel - Re: [PATCH] rcu: Use the proper lockdep annotation in dump_blkd

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Message-Id: <20180312014709.GL3918@linux.vnet.ibm.com>
Date:   Sun, 11 Mar 2018 18:47:09 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH] rcu: Use the proper lockdep annotation in
 dump_blkd_tasks()

On Fri, Mar 09, 2018 at 09:32:18AM +0800, Boqun Feng wrote:
> Sparse reported this:
> 
> | kernel/rcu/tree_plugin.h:814:9: warning: incorrect type in argument 1 (different modifiers)
> | kernel/rcu/tree_plugin.h:814:9:    expected struct lockdep_map const *lock
> | kernel/rcu/tree_plugin.h:814:9:    got struct lockdep_map [noderef] *<noident>
> 
> This is caused by using vanilla lockdep annotations on rcu_node::lock,
> and that requires accessing ->lock of rcu_node directly. However we need
> to keep rcu_node::lock __private to avoid breaking its extra ordering
> guarantee. And we have a dedicated lockdep annotation for
> rcu_node::lock, so use it.
> 
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>

Good eyes!  Queued both this and v3 for testing and further review.

							Thanx, Paul

> ---
>  kernel/rcu/tree_plugin.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 9accacffd138..ea33f57abae5 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -811,7 +811,7 @@ static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
>  	int i;
>  	struct list_head *lhp;
> 
> -	lockdep_assert_held(&rnp->lock);
> +	raw_lockdep_assert_held_rcu_node(rnp);
>  	pr_info("%s: grp: %d-%d level: %d ->qamask %#lx ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p &->blkd_tasks: %p offset: %u\n", __func__, rnp->grplo, rnp->grphi, rnp->level, rnp->qsmask, rnp->gp_tasks, rnp->boost_tasks, rnp->exp_tasks, &rnp->blkd_tasks, (unsigned int)offsetof(typeof(*rnp), blkd_tasks));
>  	pr_cont("\t->blkd_tasks");
>  	i = 0;
> -- 
> 2.16.2
>