linux-kernel - Re: [PATCH] tcm_fc: rcu_deref outside rcu lock/unlock section

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Date:	Sat, 18 Aug 2012 15:35:31 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Denis Efremov <yefremov.denis@...il.com>
Cc:	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	Jesper Juhl <jj@...osbits.net>, target-devel@...r.kernel.org,
	linux-kernel@...r.kernel.org, ldv-project@...ras.ru,
	"Rustad, Mark D" <mark.d.rustad@...el.com>,
	"Patil, Kiran" <kiran.patil@...el.com>
Subject: Re: [PATCH] tcm_fc: rcu_deref outside rcu lock/unlock section

On Sat, 2012-08-18 at 16:10 +0400, Denis Efremov wrote:
> Use rcu_dereference_protected in order to prevent lockdep
> complaint. Sequel of the patch 863555be
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Signed-off-by: Denis Efremov <yefremov.denis@...il.com>
> ---
>  drivers/target/tcm_fc/tfc_sess.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/target/tcm_fc/tfc_sess.c b/drivers/target/tcm_fc/tfc_sess.c
> index 87901fa..3c9e5b5 100644
> --- a/drivers/target/tcm_fc/tfc_sess.c
> +++ b/drivers/target/tcm_fc/tfc_sess.c
> @@ -456,7 +456,9 @@ static void ft_prlo(struct fc_rport_priv *rdata)
>  	struct ft_tport *tport;
>  
>  	mutex_lock(&ft_lport_lock);
> -	tport = rcu_dereference(rdata->local_port->prov[FC_TYPE_FCP]);
> +	tport = rcu_dereference_protected(rdata->local_port->prov[FC_TYPE_FCP],
> +					  lockdep_is_held(&ft_lport_lock));
> +
>  	if (!tport) {
>  		mutex_unlock(&ft_lport_lock);
>  		return;

This looks OK to silence lockdep.  CC'ing MDR + Kiran for good measure
here, and will move from target-pending queue -> master with their ACK.

Thanks Dennis!

--nab

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