* [PATCH] hlist_add_tail_rcu disable sparse warning
@ 2017-02-10 17:39 Michael S. Tsirkin
2017-02-27 18:26 ` Michael S. Tsirkin
2017-02-27 18:40 ` Steven Rostedt
0 siblings, 2 replies; 5+ messages in thread
From: Michael S. Tsirkin @ 2017-02-10 17:39 UTC (permalink / raw)
To: linux-kernel
Cc: Paul E. McKenney, Josh Triplett, Steven Rostedt,
Mathieu Desnoyers, Lai Jiangshan, David Miller
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>
---
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] hlist_add_tail_rcu disable sparse warning
2017-02-10 17:39 [PATCH] hlist_add_tail_rcu disable sparse warning Michael S. Tsirkin
@ 2017-02-27 18:26 ` Michael S. Tsirkin
2017-04-26 13:13 ` Steven Rostedt
2017-02-27 18:40 ` Steven Rostedt
1 sibling, 1 reply; 5+ messages in thread
From: Michael S. Tsirkin @ 2017-02-27 18:26 UTC (permalink / raw)
To: linux-kernel
Cc: Paul E. McKenney, Josh Triplett, Steven Rostedt,
Mathieu Desnoyers, Lai Jiangshan, David Miller
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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] hlist_add_tail_rcu disable sparse warning
2017-02-10 17:39 [PATCH] hlist_add_tail_rcu disable sparse warning Michael S. Tsirkin
2017-02-27 18:26 ` Michael S. Tsirkin
@ 2017-02-27 18:40 ` Steven Rostedt
1 sibling, 0 replies; 5+ messages in thread
From: Steven Rostedt @ 2017-02-27 18:40 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: linux-kernel, Paul E. McKenney, Josh Triplett, Mathieu Desnoyers,
Lai Jiangshan, David Miller
On Fri, 10 Feb 2017 19:39:49 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:
> 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)
Looks good to me, but I would probably add a comment above the loop
about this being in a write side section, and rcu conversions are not
needed.
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
> last = i;
>
> if (last) {
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] hlist_add_tail_rcu disable sparse warning
2017-02-27 18:26 ` Michael S. Tsirkin
@ 2017-04-26 13:13 ` Steven Rostedt
2017-04-26 14:02 ` Paul E. McKenney
0 siblings, 1 reply; 5+ messages in thread
From: Steven Rostedt @ 2017-04-26 13:13 UTC (permalink / raw)
To: Paul E. McKenney
Cc: Michael S. Tsirkin, linux-kernel, Josh Triplett,
Mathieu Desnoyers, Lai Jiangshan, David Miller
Paul,
Did you see this email?
-- Steve
On Mon, 27 Feb 2017 20:26:01 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:
> 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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] hlist_add_tail_rcu disable sparse warning
2017-04-26 13:13 ` Steven Rostedt
@ 2017-04-26 14:02 ` Paul E. McKenney
0 siblings, 0 replies; 5+ messages in thread
From: Paul E. McKenney @ 2017-04-26 14:02 UTC (permalink / raw)
To: Steven Rostedt
Cc: Michael S. Tsirkin, linux-kernel, Josh Triplett,
Mathieu Desnoyers, Lai Jiangshan, David Miller
On Wed, Apr 26, 2017 at 09:13:43AM -0400, Steven Rostedt wrote:
>
> Paul,
>
> Did you see this email?
Yep! Michael's patch is 48ac34666ff7 ("hlist_add_tail_rcu disable sparse
warning") in -rcu and now in -tip.
But I do appreciate the reminder -- way too easy to miss stuff on LKML!
Thanx, Paul
> -- Steve
>
>
> On Mon, 27 Feb 2017 20:26:01 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
>
> > 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
>
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2017-04-26 14:03 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2017-02-10 17:39 [PATCH] hlist_add_tail_rcu disable sparse warning Michael S. Tsirkin
2017-02-27 18:26 ` Michael S. Tsirkin
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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