diff mbox series

[v2,net-next,10/15] net/sched: make stab available before ops->init() call

Message ID 20230207135440.1482856-11-vladimir.oltean@nxp.com
State New
Headers
Series taprio automatic queueMaxSDU and new TXQ selection procedure |

Commit Message

Vladimir Oltean Feb. 7, 2023, 1:54 p.m. UTC 
  Some qdiscs like taprio turn out to be actually pretty reliant on a well
configured stab, to not underestimate the skb transmission time (by
properly accounting for L1 overhead).

In a future change, taprio will need the stab, if configured by the
user, to be available at ops->init() time. It will become even more
important in upcoming work, when the overhead will be used for the
queueMaxSDU calculation that is passed to an offloading driver.

However, rcu_assign_pointer(sch->stab, stab) is called right after
ops->init(), making it unavailable, and I don't really see a good reason
for that.

Move it earlier, which nicely seems to simplify the error handling path
as well.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
---
v1->v2: none

 net/sched/sch_api.c | 29 +++++++++++------------------
 1 file changed, 11 insertions(+), 18 deletions(-)

Comments

Eric Dumazet Feb. 10, 2023, 3:07 p.m. UTC | #1 
On Tue, Feb 7, 2023 at 2:55 PM Vladimir Oltean <vladimir.oltean@nxp.com> wrote:
>
> Some qdiscs like taprio turn out to be actually pretty reliant on a well
> configured stab, to not underestimate the skb transmission time (by
> properly accounting for L1 overhead).
>
> In a future change, taprio will need the stab, if configured by the
> user, to be available at ops->init() time. It will become even more
> important in upcoming work, when the overhead will be used for the
> queueMaxSDU calculation that is passed to an offloading driver.
>
> However, rcu_assign_pointer(sch->stab, stab) is called right after
> ops->init(), making it unavailable, and I don't really see a good reason
> for that.
>
> Move it earlier, which nicely seems to simplify the error handling path
> as well.

Well... if you say so :)

>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
>

If TCA_STAB attribute is malformed, we end up calling ->destroy() on a
not yet initialized qdisc :/

I am going to send the following fix, unless someone disagrees.

(Moving qdisc_put_stab() _after_ ops->destroy(sch) is not strictly
needed for a fix,
but undo should be done in reverse steps for clarity.

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index e9780631b5b58202068e20c42ccf1197eac2194c..aba789c30a2eb50d339b8a888495b794825e1775
100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1286,7 +1286,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
                stab = qdisc_get_stab(tca[TCA_STAB], extack);
                if (IS_ERR(stab)) {
                        err = PTR_ERR(stab);
-                       goto err_out4;
+                       goto err_out3;
                }
                rcu_assign_pointer(sch->stab, stab);
        }
@@ -1294,14 +1294,14 @@ static struct Qdisc *qdisc_create(struct
net_device *dev,
        if (ops->init) {
                err = ops->init(sch, tca[TCA_OPTIONS], extack);
                if (err != 0)
-                       goto err_out5;
+                       goto err_out4;
        }

        if (tca[TCA_RATE]) {
                err = -EOPNOTSUPP;
                if (sch->flags & TCQ_F_MQROOT) {
                        NL_SET_ERR_MSG(extack, "Cannot attach rate
estimator to a multi-queue root qdisc");
-                       goto err_out5;
+                       goto err_out4;
                }

                err = gen_new_estimator(&sch->bstats,
@@ -1312,7 +1312,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
                                        tca[TCA_RATE]);
                if (err) {
                        NL_SET_ERR_MSG(extack, "Failed to generate new
estimator");
-                       goto err_out5;
+                       goto err_out4;
                }
        }

@@ -1321,12 +1321,13 @@ static struct Qdisc *qdisc_create(struct
net_device *dev,

        return sch;

-err_out5:
-       qdisc_put_stab(rtnl_dereference(sch->stab));
 err_out4:
-       /* ops->init() failed, we call ->destroy() like qdisc_create_dflt() */
+       /* Even if ops->init() failed, we call ops->destroy()
+        * like qdisc_create_dflt().
+        */
        if (ops->destroy)
                ops->destroy(sch);
+       qdisc_put_stab(rtnl_dereference(sch->stab));
 err_out3:
        netdev_put(dev, &sch->dev_tracker);
        qdisc_free(sch);
Vladimir Oltean Feb. 10, 2023, 3:20 p.m. UTC | #2 
On Fri, Feb 10, 2023 at 04:07:42PM +0100, Eric Dumazet wrote:
> On Tue, Feb 7, 2023 at 2:55 PM Vladimir Oltean <vladimir.oltean@nxp.com> wrote:
> > Move it earlier, which nicely seems to simplify the error handling path
> > as well.
> 
> Well... if you say so :)

:)

> If TCA_STAB attribute is malformed, we end up calling ->destroy() on a
> not yet initialized qdisc :/

Right. Sorry, I didn't pay enough attention, and the old structure with
"err_out4" having a "goto err_out3" confused me. Because I was trying to
match the old teardown path with the new (linear) one, I was trying to
keep the order between qdisc_put_stab() and ops->destroy(). But I forgot
that I need to *reverse* it, since I reversed their order in the setup
path :-/

> I am going to send the following fix, unless someone disagrees.
> 
> (Moving qdisc_put_stab() _after_ ops->destroy(sch) is not strictly
> needed for a fix,
> but undo should be done in reverse steps for clarity.

Right, and it's a net-next patch, so a larger fix which brings the code
into shape should be fine.

> 
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index e9780631b5b58202068e20c42ccf1197eac2194c..aba789c30a2eb50d339b8a888495b794825e1775
> 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -1286,7 +1286,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
>                 stab = qdisc_get_stab(tca[TCA_STAB], extack);
>                 if (IS_ERR(stab)) {
>                         err = PTR_ERR(stab);
> -                       goto err_out4;
> +                       goto err_out3;
>                 }
>                 rcu_assign_pointer(sch->stab, stab);
>         }
> @@ -1294,14 +1294,14 @@ static struct Qdisc *qdisc_create(struct
> net_device *dev,
>         if (ops->init) {
>                 err = ops->init(sch, tca[TCA_OPTIONS], extack);
>                 if (err != 0)
> -                       goto err_out5;
> +                       goto err_out4;
>         }
> 
>         if (tca[TCA_RATE]) {
>                 err = -EOPNOTSUPP;
>                 if (sch->flags & TCQ_F_MQROOT) {
>                         NL_SET_ERR_MSG(extack, "Cannot attach rate
> estimator to a multi-queue root qdisc");
> -                       goto err_out5;
> +                       goto err_out4;
>                 }
> 
>                 err = gen_new_estimator(&sch->bstats,
> @@ -1312,7 +1312,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
>                                         tca[TCA_RATE]);
>                 if (err) {
>                         NL_SET_ERR_MSG(extack, "Failed to generate new
> estimator");
> -                       goto err_out5;
> +                       goto err_out4;
>                 }
>         }
> 
> @@ -1321,12 +1321,13 @@ static struct Qdisc *qdisc_create(struct
> net_device *dev,
> 
>         return sch;
> 
> -err_out5:
> -       qdisc_put_stab(rtnl_dereference(sch->stab));
>  err_out4:
> -       /* ops->init() failed, we call ->destroy() like qdisc_create_dflt() */
> +       /* Even if ops->init() failed, we call ops->destroy()
> +        * like qdisc_create_dflt().
> +        */
>         if (ops->destroy)
>                 ops->destroy(sch);
> +       qdisc_put_stab(rtnl_dereference(sch->stab));
>  err_out3:
>         netdev_put(dev, &sch->dev_tracker);
>         qdisc_free(sch);

I applied the changes from this patch manually, and the result looks good.
Thanks (and sorry)!
diff mbox series

Patch

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index c14018a8052c..e9780631b5b5 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1282,12 +1282,6 @@  static struct Qdisc *qdisc_create(struct net_device *dev,
 	if (err)
 		goto err_out3;
 
-	if (ops->init) {
-		err = ops->init(sch, tca[TCA_OPTIONS], extack);
-		if (err != 0)
-			goto err_out5;
-	}
-
 	if (tca[TCA_STAB]) {
 		stab = qdisc_get_stab(tca[TCA_STAB], extack);
 		if (IS_ERR(stab)) {
@@ -1296,11 +1290,18 @@  static struct Qdisc *qdisc_create(struct net_device *dev,
 		}
 		rcu_assign_pointer(sch->stab, stab);
 	}
+
+	if (ops->init) {
+		err = ops->init(sch, tca[TCA_OPTIONS], extack);
+		if (err != 0)
+			goto err_out5;
+	}
+
 	if (tca[TCA_RATE]) {
 		err = -EOPNOTSUPP;
 		if (sch->flags & TCQ_F_MQROOT) {
 			NL_SET_ERR_MSG(extack, "Cannot attach rate estimator to a multi-queue root qdisc");
-			goto err_out4;
+			goto err_out5;
 		}
 
 		err = gen_new_estimator(&sch->bstats,
@@ -1311,7 +1312,7 @@  static struct Qdisc *qdisc_create(struct net_device *dev,
 					tca[TCA_RATE]);
 		if (err) {
 			NL_SET_ERR_MSG(extack, "Failed to generate new estimator");
-			goto err_out4;
+			goto err_out5;
 		}
 	}
 
@@ -1321,6 +1322,8 @@  static struct Qdisc *qdisc_create(struct net_device *dev,
 	return sch;
 
 err_out5:
+	qdisc_put_stab(rtnl_dereference(sch->stab));
+err_out4:
 	/* ops->init() failed, we call ->destroy() like qdisc_create_dflt() */
 	if (ops->destroy)
 		ops->destroy(sch);
@@ -1332,16 +1335,6 @@  static struct Qdisc *qdisc_create(struct net_device *dev,
 err_out:
 	*errp = err;
 	return NULL;
-
-err_out4:
-	/*
-	 * Any broken qdiscs that would require a ops->reset() here?
-	 * The qdisc was never in action so it shouldn't be necessary.
-	 */
-	qdisc_put_stab(rtnl_dereference(sch->stab));
-	if (ops->destroy)
-		ops->destroy(sch);
-	goto err_out3;
 }
 
 static int qdisc_change(struct Qdisc *sch, struct nlattr **tca,