* [PATCH v2] hlist_add_tail_rcu disable sparse warning
@ 2017-02-27 19:14 Michael S. Tsirkin
2017-03-01 19:37 ` Paul E. McKenney
0 siblings, 1 reply; 2+ messages in thread
From: Michael S. Tsirkin @ 2017-02-27 19:14 UTC (permalink / raw)
To: linux-kernel
Cc: Steven Rostedt, Paul E. McKenney, Josh Triplett,
Mathieu Desnoyers, Lai Jiangshan
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>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
Comments from v2:
add a comment as requested by Steven Rostedt
include/linux/rculist.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 4f7a956..b1fd8bf 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -509,7 +509,8 @@ 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))
+ /* Note: write side code, so rcu accessors are not needed. */
+ for (i = h->first; i; i = i->next)
last = i;
if (last) {
--
MST
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] hlist_add_tail_rcu disable sparse warning
2017-02-27 19:14 [PATCH v2] hlist_add_tail_rcu disable sparse warning Michael S. Tsirkin
@ 2017-03-01 19:37 ` Paul E. McKenney
0 siblings, 0 replies; 2+ messages in thread
From: Paul E. McKenney @ 2017-03-01 19:37 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, Steven Rostedt, Josh Triplett, Mathieu Desnoyers,
Lai Jiangshan
On Mon, Feb 27, 2017 at 09:14:19PM +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>
> Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Queud for further review and testing, thank you both!
Thanx, Paul
> ---
>
> Comments from v2:
> add a comment as requested by Steven Rostedt
>
> include/linux/rculist.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index 4f7a956..b1fd8bf 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -509,7 +509,8 @@ 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))
> + /* Note: write side code, so rcu accessors are not needed. */
> + for (i = h->first; i; i = i->next)
> last = i;
>
> if (last) {
> --
> MST
>
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