From: "Michael S. Tsirkin" <mst@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
David Miller <davem@davemloft.net>
Subject: Re: [PATCH] hlist_add_tail_rcu disable sparse warning
Date: Mon, 27 Feb 2017 20:26:01 +0200 [thread overview]
Message-ID: <20170227202547-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <1486748308-16653-1-git-send-email-mst@redhat.com>
On Fri, Feb 10, 2017 at 07:39:49PM +0200, Michael S. Tsirkin wrote:
> sparse is unhappy about this code in hlist_add_tail_rcu:
>
> struct hlist_node *i, *last = NULL;
>
> for (i = hlist_first_rcu(h); i; i = hlist_next_rcu(i))
> last = i;
>
> This is because hlist_next_rcu and hlist_next_rcu return
> __rcu pointers.
>
> It's a false positive - it's a write side primitive and so
> does not need to be called in a read side critical section.
>
> The following trivial patch disables the warning
> without changing the behaviour in any way.
>
> Note: __hlist_for_each_rcu would also remove the warning but it would be
> confusing since it calls rcu_derefence and is designed to run in the rcu
> read side critical section.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
ping
> changes since RFC
> added commit log text to explain why don't we use __hlist_for_each_rcu
>
> include/linux/rculist.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index 4f7a956..bf578e8 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -509,7 +509,7 @@ static inline void hlist_add_tail_rcu(struct hlist_node *n,
> {
> struct hlist_node *i, *last = NULL;
>
> - for (i = hlist_first_rcu(h); i; i = hlist_next_rcu(i))
> + for (i = h->first; i; i = i->next)
> last = i;
>
> if (last) {
> --
> MST
next prev parent reply other threads:[~2017-02-27 18:51 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-10 17:39 [PATCH] hlist_add_tail_rcu disable sparse warning Michael S. Tsirkin
2017-02-27 18:26 ` Michael S. Tsirkin [this message]
2017-04-26 13:13 ` Steven Rostedt
2017-04-26 14:02 ` Paul E. McKenney
2017-02-27 18:40 ` Steven Rostedt
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