[PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount

[PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount

[Chuhong Yuan]

refcount_t is better for reference counters since its
implementation can prevent overflows.
So convert atomic_t ref counters to refcount_t.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
---
Changes in v2:
  - Convert refcount from 0-base to 1-base.

 drivers/net/ethernet/chelsio/cxgb4/sched.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb4/sched.c b/drivers/net/ethernet/chelsio/cxgb4/sched.c
index 60218dc676a8..0d902d125be4 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/sched.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/sched.c
@@ -173,7 +173,7 @@ static int t4_sched_queue_unbind(struct port_info *pi, struct ch_sched_queue *p)
 
 		list_del(&qe->list);
 		kvfree(qe);
-		if (atomic_dec_and_test(&e->refcnt)) {
+		if (refcount_dec_and_test(&e->refcnt)) {
 			e->state = SCHED_STATE_UNUSED;
 			memset(&e->info, 0, sizeof(e->info));
 		}
@@ -216,7 +216,7 @@ static int t4_sched_queue_bind(struct port_info *pi, struct ch_sched_queue *p)
 		goto out_err;
 
 	list_add_tail(&qe->list, &e->queue_list);
-	atomic_inc(&e->refcnt);
+	refcount_inc(&e->refcnt);
 	return err;
 
 out_err:
@@ -434,7 +434,7 @@ static struct sched_class *t4_sched_class_alloc(struct port_info *pi,
 		if (err)
 			return NULL;
 		memcpy(&e->info, &np, sizeof(e->info));
-		atomic_set(&e->refcnt, 0);
+		refcount_set(&e->refcnt, 1);
 		e->state = SCHED_STATE_ACTIVE;
 	}
 
@@ -488,7 +488,7 @@ struct sched_table *t4_init_sched(unsigned int sched_size)
 		s->tab[i].idx = i;
 		s->tab[i].state = SCHED_STATE_UNUSED;
 		INIT_LIST_HEAD(&s->tab[i].queue_list);
-		atomic_set(&s->tab[i].refcnt, 0);
+		refcount_set(&s->tab[i].refcnt, 1);
 	}
 	return s;
 }
-- 
2.20.1

Re: [PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount

[Willem de Bruijn]

On Fri, Aug 2, 2019 at 4:36 AM Chuhong Yuan <hslester96@gmail.com> wrote:
>
> refcount_t is better for reference counters since its
> implementation can prevent overflows.
> So convert atomic_t ref counters to refcount_t.
>
> Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
> ---
> Changes in v2:
>   - Convert refcount from 0-base to 1-base.

This changes the initial value from 0 to 1, but does not change the
release condition. So this introduces an accounting bug?

Re: [PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount

[Chuhong Yuan]

Willem de Bruijn <willemdebruijn.kernel@gmail.com> 于2019年8月2日周五 下午9:40写道：
>
> On Fri, Aug 2, 2019 at 4:36 AM Chuhong Yuan <hslester96@gmail.com> wrote:
> >
> > refcount_t is better for reference counters since its
> > implementation can prevent overflows.
> > So convert atomic_t ref counters to refcount_t.
> >
> > Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
> > ---
> > Changes in v2:
> >   - Convert refcount from 0-base to 1-base.
>
> This changes the initial value from 0 to 1, but does not change the
> release condition. So this introduces an accounting bug?

I have noticed this problem and have checked other files which use refcount_t.
I find although the refcounts are 1-based, they still use
refcount_dec_and_test()
to check whether the resource should be released.
One example is drivers/char/mspec.c.
Therefore I think this is okay and do not change the release condition.

Re: [PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount

[Willem de Bruijn]

On Fri, Aug 2, 2019 at 10:27 AM Chuhong Yuan <hslester96@gmail.com> wrote:
>
> Willem de Bruijn <willemdebruijn.kernel@gmail.com> 于2019年8月2日周五 下午9:40写道：
> >
> > On Fri, Aug 2, 2019 at 4:36 AM Chuhong Yuan <hslester96@gmail.com> wrote:
> > >
> > > refcount_t is better for reference counters since its
> > > implementation can prevent overflows.
> > > So convert atomic_t ref counters to refcount_t.
> > >
> > > Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
> > > ---
> > > Changes in v2:
> > >   - Convert refcount from 0-base to 1-base.
> >
> > This changes the initial value from 0 to 1, but does not change the
> > release condition. So this introduces an accounting bug?
>
> I have noticed this problem and have checked other files which use refcount_t.
> I find although the refcounts are 1-based, they still use
> refcount_dec_and_test()
> to check whether the resource should be released.
> One example is drivers/char/mspec.c.
> Therefore I think this is okay and do not change the release condition.

Indeed it is fine to use refcount_t with a model where the initial
allocation already accounts for the first reference and thus
initializes with refcount_set(.., 1).

But it is not correct to just change a previously zero initialization
to one. As now an extra refcount_dec will be needed to release state.
But the rest of the code has not changed, so this extra decrement will
not happen.

For a correct conversion, see for instance commits

  commit db5bce32fbe19f0c7482fb5a40a33178bbe7b11b
  net: prepare (struct ubuf_info)->refcnt conversion

and

  commit c1d1b437816f0afa99202be3cb650c9d174667bc
  net: convert (struct ubuf_info)->refcnt to refcount_t

The second makes a search-and-replace style API change like your
patches (though also notice the additional required #include).

But the other patch is needed first to change both the initial
atomic_set *and* at least one atomic_inc, to maintain the same
reference count over the object's lifetime.

That change requires understanding of the object's lifecycle, so I
suggest only making those changes when aware of that whole data path.

Re: [PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount

[Chuhong Yuan]

Willem de Bruijn <willemdebruijn.kernel@gmail.com> 于2019年8月2日周五 下午10:53写道：
>
> On Fri, Aug 2, 2019 at 10:27 AM Chuhong Yuan <hslester96@gmail.com> wrote:
> >
> > Willem de Bruijn <willemdebruijn.kernel@gmail.com> 于2019年8月2日周五 下午9:40写道：
> > >
> > > On Fri, Aug 2, 2019 at 4:36 AM Chuhong Yuan <hslester96@gmail.com> wrote:
> > > >
> > > > refcount_t is better for reference counters since its
> > > > implementation can prevent overflows.
> > > > So convert atomic_t ref counters to refcount_t.
> > > >
> > > > Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
> > > > ---
> > > > Changes in v2:
> > > >   - Convert refcount from 0-base to 1-base.
> > >
> > > This changes the initial value from 0 to 1, but does not change the
> > > release condition. So this introduces an accounting bug?
> >
> > I have noticed this problem and have checked other files which use refcount_t.
> > I find although the refcounts are 1-based, they still use
> > refcount_dec_and_test()
> > to check whether the resource should be released.
> > One example is drivers/char/mspec.c.
> > Therefore I think this is okay and do not change the release condition.
>
> Indeed it is fine to use refcount_t with a model where the initial
> allocation already accounts for the first reference and thus
> initializes with refcount_set(.., 1).
>
> But it is not correct to just change a previously zero initialization
> to one. As now an extra refcount_dec will be needed to release state.
> But the rest of the code has not changed, so this extra decrement will
> not happen.
>
> For a correct conversion, see for instance commits
>
>   commit db5bce32fbe19f0c7482fb5a40a33178bbe7b11b
>   net: prepare (struct ubuf_info)->refcnt conversion
>
> and
>
>   commit c1d1b437816f0afa99202be3cb650c9d174667bc
>   net: convert (struct ubuf_info)->refcnt to refcount_t
>
> The second makes a search-and-replace style API change like your
> patches (though also notice the additional required #include).
>

Thanks for your examples!
I will fix the #include in those no base changed patches.

> But the other patch is needed first to change both the initial
> atomic_set *and* at least one atomic_inc, to maintain the same
> reference count over the object's lifetime.
>
> That change requires understanding of the object's lifecycle, so I
> suggest only making those changes when aware of that whole data path.

I think I had better focus on the 1-based cases first.

Re: [PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount

[Willem de Bruijn]

On Fri, Aug 2, 2019 at 11:10 AM Chuhong Yuan <hslester96@gmail.com> wrote:
>
> Willem de Bruijn <willemdebruijn.kernel@gmail.com> 于2019年8月2日周五 下午10:53写道：
> >
> > On Fri, Aug 2, 2019 at 10:27 AM Chuhong Yuan <hslester96@gmail.com> wrote:
> > >
> > > Willem de Bruijn <willemdebruijn.kernel@gmail.com> 于2019年8月2日周五 下午9:40写道：
> > > >
> > > > On Fri, Aug 2, 2019 at 4:36 AM Chuhong Yuan <hslester96@gmail.com> wrote:
> > > > >
> > > > > refcount_t is better for reference counters since its
> > > > > implementation can prevent overflows.
> > > > > So convert atomic_t ref counters to refcount_t.
> > > > >
> > > > > Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
> > > > > ---
> > > > > Changes in v2:
> > > > >   - Convert refcount from 0-base to 1-base.
> > > >
> > > > This changes the initial value from 0 to 1, but does not change the
> > > > release condition. So this introduces an accounting bug?
> > >
> > > I have noticed this problem and have checked other files which use refcount_t.
> > > I find although the refcounts are 1-based, they still use
> > > refcount_dec_and_test()
> > > to check whether the resource should be released.
> > > One example is drivers/char/mspec.c.
> > > Therefore I think this is okay and do not change the release condition.
> >
> > Indeed it is fine to use refcount_t with a model where the initial
> > allocation already accounts for the first reference and thus
> > initializes with refcount_set(.., 1).
> >
> > But it is not correct to just change a previously zero initialization
> > to one. As now an extra refcount_dec will be needed to release state.
> > But the rest of the code has not changed, so this extra decrement will
> > not happen.
> >
> > For a correct conversion, see for instance commits
> >
> >   commit db5bce32fbe19f0c7482fb5a40a33178bbe7b11b
> >   net: prepare (struct ubuf_info)->refcnt conversion
> >
> > and
> >
> >   commit c1d1b437816f0afa99202be3cb650c9d174667bc
> >   net: convert (struct ubuf_info)->refcnt to refcount_t
> >
> > The second makes a search-and-replace style API change like your
> > patches (though also notice the additional required #include).
> >
>
> Thanks for your examples!
> I will fix the #include in those no base changed patches.
>
> > But the other patch is needed first to change both the initial
> > atomic_set *and* at least one atomic_inc, to maintain the same
> > reference count over the object's lifetime.
> >
> > That change requires understanding of the object's lifecycle, so I
> > suggest only making those changes when aware of that whole data path.
>
> I think I had better focus on the 1-based cases first.

Yes, sounds good. And please try a single driver first and get that
accepted, before moving on to multiple concurrent submissions.

[PATCH v2 1/2] cxgb4: sched: Use refcount_t for refcount

[Chuhong Yuan]

refcount_t is better for reference counters since its
implementation can prevent overflows.
So convert atomic_t ref counters to refcount_t.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
---
Changes in v2:
  - Convert refcount from 0-base to 1-base.

 drivers/net/ethernet/chelsio/cxgb4/sched.c | 8 ++++----
 drivers/net/ethernet/chelsio/cxgb4/sched.h | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb4/sched.c b/drivers/net/ethernet/chelsio/cxgb4/sched.c
index 60218dc676a8..0d902d125be4 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/sched.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/sched.c
@@ -173,7 +173,7 @@ static int t4_sched_queue_unbind(struct port_info *pi, struct ch_sched_queue *p)
 
 		list_del(&qe->list);
 		kvfree(qe);
-		if (atomic_dec_and_test(&e->refcnt)) {
+		if (refcount_dec_and_test(&e->refcnt)) {
 			e->state = SCHED_STATE_UNUSED;
 			memset(&e->info, 0, sizeof(e->info));
 		}
@@ -216,7 +216,7 @@ static int t4_sched_queue_bind(struct port_info *pi, struct ch_sched_queue *p)
 		goto out_err;
 
 	list_add_tail(&qe->list, &e->queue_list);
-	atomic_inc(&e->refcnt);
+	refcount_inc(&e->refcnt);
 	return err;
 
 out_err:
@@ -434,7 +434,7 @@ static struct sched_class *t4_sched_class_alloc(struct port_info *pi,
 		if (err)
 			return NULL;
 		memcpy(&e->info, &np, sizeof(e->info));
-		atomic_set(&e->refcnt, 0);
+		refcount_set(&e->refcnt, 1);
 		e->state = SCHED_STATE_ACTIVE;
 	}
 
@@ -488,7 +488,7 @@ struct sched_table *t4_init_sched(unsigned int sched_size)
 		s->tab[i].idx = i;
 		s->tab[i].state = SCHED_STATE_UNUSED;
 		INIT_LIST_HEAD(&s->tab[i].queue_list);
-		atomic_set(&s->tab[i].refcnt, 0);
+		refcount_set(&s->tab[i].refcnt, 1);
 	}
 	return s;
 }
diff --git a/drivers/net/ethernet/chelsio/cxgb4/sched.h b/drivers/net/ethernet/chelsio/cxgb4/sched.h
index 168fb4ce3759..23a6ca1e6d3e 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/sched.h
+++ b/drivers/net/ethernet/chelsio/cxgb4/sched.h
@@ -69,7 +69,7 @@ struct sched_class {
 	u8 idx;
 	struct ch_sched_params info;
 	struct list_head queue_list;
-	atomic_t refcnt;
+	refcount_t refcnt;
 };
 
 struct sched_table {      /* per port scheduling table */
-- 
2.20.1