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 <[email protected]>
---
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
On Fri, Aug 2, 2019 at 4:36 AM Chuhong Yuan <[email protected]> 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 <[email protected]>
> ---
> 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?
Willem de Bruijn <[email protected]> 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 <[email protected]> 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 <[email protected]>
> > ---
> > 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.
On Fri, Aug 2, 2019 at 10:27 AM Chuhong Yuan <[email protected]> wrote:
>
> Willem de Bruijn <[email protected]> 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 <[email protected]> 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 <[email protected]>
> > > ---
> > > 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.