[PATCH] rtnl_unlock/lock in sch_api.c TRY3

[PATCH] rtnl_unlock/lock in sch_api.c TRY3

[Catalin(ux aka Dino) BOIE]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 671 bytes --]

Hello!

Trying to load a custom module (same for teql but I didn't tried it)
whan the qdisc module is not loaded, makes tc hang.
This is because qdisc_create aquires rtnl_sem and then tries to load a module 
that tries to register_netdev (that tries to aquire the same rtnl_sem).
Applying this patch makes the problem go away.

The patch was tested under 2.6.11.6.

Signed-off-by: Catalin(ux aka Dino) BOIE <catab at umbrella.ro>

Please apply.

The patch is a rewrite of Dave's one with small additions (module_put 
in and dev_put out).

Thanks for help goes to Dave, Thomas and Patrick.

---
Catalin(ux aka Dino) BOIE
catab at deuroconsult.ro
http://kernel.umbrella.ro/

[-- Attachment #2: Type: TEXT/PLAIN, Size: 2046 bytes --]

--- linux-2.6/net/sched/sch_api.c.orig	2005-03-29 01:20:18.000000000 +0300
+++ linux-2.6/net/sched/sch_api.c	2005-03-31 22:44:41.000000000 +0300
@@ -406,11 +406,29 @@ qdisc_create(struct net_device *dev, u32
 
 	ops = qdisc_lookup_ops(kind);
 #ifdef CONFIG_KMOD
-	if (ops==NULL && tca[TCA_KIND-1] != NULL) {
+	if (ops == NULL && kind != NULL) {
 		char name[IFNAMSIZ];
 		if (rtattr_strlcpy(name, kind, IFNAMSIZ) < IFNAMSIZ) {
+			/* We dropped the RTNL semaphore in order to
+			 * perform the module load.  So, even if we
+			 * succeeded in loading the module we have to
+			 * tell the caller to replay the request.  We
+			 * indicate this using -EAGAIN.
+			 * We replay the request because the device may
+			 * go away in the mean time.
+			 */
+			rtnl_unlock();
 			request_module("sch_%s", name);
+			rtnl_lock();
 			ops = qdisc_lookup_ops(kind);
+			if (ops != NULL) {
+				/* We will try again qdisc_lookup_ops,
+				 * so don't keep a reference.
+				 */
+				module_put(ops->owner);
+				err = -EAGAIN;
+				goto err_out;
+			}
 		}
 	}
 #endif
@@ -606,14 +624,20 @@ static int tc_get_qdisc(struct sk_buff *
 
 static int tc_modify_qdisc(struct sk_buff *skb, struct nlmsghdr *n, void *arg)
 {
-	struct tcmsg *tcm = NLMSG_DATA(n);
-	struct rtattr **tca = arg;
+	struct tcmsg *tcm;
+	struct rtattr **tca;
 	struct net_device *dev;
-	u32 clid = tcm->tcm_parent;
-	struct Qdisc *q = NULL;
-	struct Qdisc *p = NULL;
+	u32 clid;
+	struct Qdisc *q, *p;
 	int err;
 
+	replay:
+	/* Reinit, just in case something touches this. */
+	tcm = NLMSG_DATA(n);
+	tca = arg;
+	clid = tcm->tcm_parent;
+	q = p = NULL;
+
 	if ((dev = __dev_get_by_index(tcm->tcm_ifindex)) == NULL)
 		return -ENODEV;
 
@@ -707,8 +731,11 @@ create_n_graft:
 		q = qdisc_create(dev, tcm->tcm_parent, tca, &err);
         else
 		q = qdisc_create(dev, tcm->tcm_handle, tca, &err);
-	if (q == NULL)
+	if (q == NULL) {
+		if (err == -EAGAIN)
+			goto replay;
 		return err;
+	}
 
 graft:
 	if (1) {

Re: [PATCH] rtnl_unlock/lock in sch_api.c TRY3

[David S. Miller]

On Thu, 31 Mar 2005 23:11:06 +0300 (EEST)
"Catalin(ux aka Dino) BOIE" <util@deuroconsult.ro> wrote:

> Hello!
> 
> Trying to load a custom module (same for teql but I didn't tried it)
> whan the qdisc module is not loaded, makes tc hang.
> This is because qdisc_create aquires rtnl_sem and then tries to load a module 
> that tries to register_netdev (that tries to aquire the same rtnl_sem).
> Applying this patch makes the problem go away.
> 
> The patch was tested under 2.6.11.6.
> 
> Signed-off-by: Catalin(ux aka Dino) BOIE <catab at umbrella.ro>
> 
> Please apply.

Looks good, applied, thanks Catalin.