netdev - Re: suspicious RCU usage (netlink/rhashtable)

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Message-Id: <20151222.155100.2233619580820015796.davem@davemloft.net>
Date:	Tue, 22 Dec 2015 15:51:00 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	davej@...emonkey.org.uk
Cc:	netdev@...r.kernel.org
Subject: Re: suspicious RCU usage (netlink/rhashtable)

From: Dave Jones <davej@...emonkey.org.uk>
Date: Tue, 22 Dec 2015 15:45:39 -0500

> ===============================
> [ INFO: suspicious RCU usage. ]
> 4.4.0-rc6-think+ #1 Not tainted
> -------------------------------
> lib/rhashtable.c:522 suspicious rcu_dereference_protected() usage!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 1, debug_locks = 0
> 2 locks held by trinity-c1/3652:
>  #0:  (&p->lock){+.+.+.}, at: [<ffffffff9a3335a7>] seq_read+0xd7/0x900
>  #1:  (&(&ht->lock)->rlock){+.+...}, at: [<ffffffff9a56f29d>] rhashtable_walk_init+0x9d/0x170

I'm so confused, the code reads:

	spin_lock(&ht->lock);
	iter->walker->tbl =
		rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));

?!?!?!
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