Subject: Re: xfrm_state locking regression...

From: Timo Teräs <[email-masked]>
Date: Wed, 24 Sep 2008 10:29:15 +0300

Herbert Xu wrote:
> On Wed, Sep 24, 2008 at 09:20:10AM +0300, Timo Teräs wrote:
>> Just saying that the code easily misleads the reader. And in
>> this kind of non-obvious places we should have some comments.
>> Or make the code more readable by adding the intermediate struct.
> 
> Fair enough.  Feel free to reformat the patch and add the struct
> to make it more bullet-proof.  I'm sorry I've got some paid work
> to do now :)

Ok, here's one try. I also updated the list_add() calls introduced
in commit "ipsec: Restore larval states and socket policies in
dump".

Same warning still applies: only compile tested.

We should probably do similar fix for the SPD dumping. I can make
a patch for that later today.

- Timo

ipsec: Put dumpers on the dump list

Based on Herbert Xu's patch and idea. Improved the original patch
to apply cleanly and modified iteration code to be more readable
by using a common struct for entries in all list.

As it is we go to extraordinary lengths to ensure that states
don't go away while dumpers go to sleep.  It's much easier if
we just put the dumpers themselves on the list since they can't
go away while they're going.

I've also changed the order of addition on new states to prevent
a never-ending dump.

Finally the obsolete last optimisation is now gone.

Signed-off-by: Herbert Xu <[email-masked]>
Signed-off-by: Timo Teras <[email-masked]>

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index cbba776..9ff1b54 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -220,7 +220,7 @@ struct netlink_callback
 	int		(*dump)(struct sk_buff * skb, struct netlink_callback *cb);
 	int		(*done)(struct netlink_callback *cb);
 	int		family;
-	long		args[7];
+	long		args[6];
 };
 
 struct netlink_notify
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 48630b2..becaa1e 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -117,12 +117,21 @@ extern struct mutex xfrm_cfg_mutex;
       metrics. Plus, it will be made via sk->sk_dst_cache. Solved.
  */
 
+struct xfrm_state_walk {
+	struct list_head	all;
+	u8			state;
+	union {
+		u8		dying;
+		u8		proto;
+	};
+	u32			seq;
+};
+
 /* Full description of state of transformer. */
 struct xfrm_state
 {
-	struct list_head	all;
 	union {
-		struct list_head	gclist;
+		struct hlist_node	gclist;
 		struct hlist_node	bydst;
 	};
 	struct hlist_node	bysrc;
@@ -136,12 +145,8 @@ struct xfrm_state
 
 	u32			genid;
 
-	/* Key manger bits */
-	struct {
-		u8		state;
-		u8		dying;
-		u32		seq;
-	} km;
+	/* Key manager bits */
+	struct xfrm_state_walk	km;
 
 	/* Parameters of this state. */
 	struct {
@@ -1245,14 +1250,6 @@ struct xfrm6_tunnel {
 	int priority;
 };
 
-struct xfrm_state_walk {
-	struct list_head list;
-	unsigned long genid;
-	struct xfrm_state *state;
-	int count;
-	u8 proto;
-};
-
 struct xfrm_policy_walk {
 	struct xfrm_policy *policy;
 	int count;
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 053970e..f2deae0 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -59,14 +59,6 @@ static unsigned int xfrm_state_hashmax __read_mostly = 1 * 1024 * 1024;
 static unsigned int xfrm_state_num;
 static unsigned int xfrm_state_genid;
 
-/* Counter indicating ongoing walk, protected by xfrm_state_lock. */
-static unsigned long xfrm_state_walk_ongoing;
-/* Counter indicating walk completion, protected by xfrm_cfg_mutex. */
-static unsigned long xfrm_state_walk_completed;
-
-/* List of outstanding state walks used to set the completed counter.  */
-static LIST_HEAD(xfrm_state_walks);
-
 static struct xfrm_state_afinfo *xfrm_state_get_afinfo(unsigned int family);
 static void xfrm_state_put_afinfo(struct xfrm_state_afinfo *afinfo);
 
@@ -199,8 +191,7 @@ static DEFINE_RWLOCK(xfrm_state_afinfo_lock);
 static struct xfrm_state_afinfo *xfrm_state_afinfo[NPROTO];
 
 static struct work_struct xfrm_state_gc_work;
-static LIST_HEAD(xfrm_state_gc_leftovers);
-static LIST_HEAD(xfrm_state_gc_list);
+static HLIST_HEAD(xfrm_state_gc_list);
 static DEFINE_SPINLOCK(xfrm_state_gc_lock);
 
 int __xfrm_state_delete(struct xfrm_state *x);
@@ -412,23 +403,16 @@ static void xfrm_state_gc_destroy(struct xfrm_state *x)
 
 static void xfrm_state_gc_task(struct work_struct *data)
 {
-	struct xfrm_state *x, *tmp;
-	unsigned long completed;
+	struct xfrm_state *x;
+	struct hlist_node *entry, *tmp;
+	struct hlist_head gc_list;
 
-	mutex_lock(&xfrm_cfg_mutex);
 	spin_lock_bh(&xfrm_state_gc_lock);
-	list_splice_tail_init(&xfrm_state_gc_list, &xfrm_state_gc_leftovers);
+	hlist_move_list(&xfrm_state_gc_list, &gc_list);
 	spin_unlock_bh(&xfrm_state_gc_lock);
 
-	completed = xfrm_state_walk_completed;
-	mutex_unlock(&xfrm_cfg_mutex);
-
-	list_for_each_entry_safe(x, tmp, &xfrm_state_gc_leftovers, gclist) {
-		if ((long)(x->lastused - completed) > 0)
-			break;
-		list_del(&x->gclist);
+	hlist_for_each_entry_safe(x, entry, tmp, &gc_list, gclist)
 		xfrm_state_gc_destroy(x);
-	}
 
 	wake_up(&km_waitq);
 }
@@ -529,7 +513,7 @@ struct xfrm_state *xfrm_state_alloc(void)
 	if (x) {
 		atomic_set(&x->refcnt, 1);
 		atomic_set(&x->tunnel_users, 0);
-		INIT_LIST_HEAD(&x->all);
+		INIT_LIST_HEAD(&x->km.all);
 		INIT_HLIST_NODE(&x->bydst);
 		INIT_HLIST_NODE(&x->bysrc);
 		INIT_HLIST_NODE(&x->byspi);
@@ -556,7 +540,7 @@ void __xfrm_state_destroy(struct xfrm_state *x)
 	WARN_ON(x->km.state != XFRM_STATE_DEAD);
 
 	spin_lock_bh(&xfrm_state_gc_lock);
-	list_add_tail(&x->gclist, &xfrm_state_gc_list);
+	hlist_add_head(&x->gclist, &xfrm_state_gc_list);
 	spin_unlock_bh(&xfrm_state_gc_lock);
 	schedule_work(&xfrm_state_gc_work);
 }
@@ -569,8 +553,7 @@ int __xfrm_state_delete(struct xfrm_state *x)
 	if (x->km.state != XFRM_STATE_DEAD) {
 		x->km.state = XFRM_STATE_DEAD;
 		spin_lock(&xfrm_state_lock);
-		x->lastused = xfrm_state_walk_ongoing;
-		list_del_rcu(&x->all);
+		list_del(&x->km.all);
 		hlist_del(&x->bydst);
 		hlist_del(&x->bysrc);
 		if (x->id.spi)
@@ -871,7 +854,7 @@ xfrm_state_find(xfrm_address_t *daddr, xfrm_address_t *saddr,
 
 		if (km_query(x, tmpl, pol) == 0) {
 			x->km.state = XFRM_STATE_ACQ;
-			list_add_tail(&x->all, &xfrm_state_all);
+			list_add(&x->km.all, &xfrm_state_all);
 			hlist_add_head(&x->bydst, xfrm_state_bydst+h);
 			h = xfrm_src_hash(daddr, saddr, family);
 			hlist_add_head(&x->bysrc, xfrm_state_bysrc+h);
@@ -940,7 +923,7 @@ static void __xfrm_state_insert(struct xfrm_state *x)
 
 	x->genid = ++xfrm_state_genid;
 
-	list_add_tail(&x->all, &xfrm_state_all);
+	list_add(&x->km.all, &xfrm_state_all);
 
 	h = xfrm_dst_hash(&x->id.daddr, &x->props.saddr,
 			  x->props.reqid, x->props.family);
@@ -1069,7 +1052,7 @@ static struct xfrm_state *__find_acq_core(unsigned short family, u8 mode, u32 re
 		xfrm_state_hold(x);
 		x->timer.expires = jiffies + sysctl_xfrm_acq_expires*HZ;
 		add_timer(&x->timer);
-		list_add_tail(&x->all, &xfrm_state_all);
+		list_add(&x->km.all, &xfrm_state_all);
 		hlist_add_head(&x->bydst, xfrm_state_bydst+h);
 		h = xfrm_src_hash(daddr, saddr, family);
 		hlist_add_head(&x->bysrc, xfrm_state_bysrc+h);
@@ -1566,79 +1549,56 @@ int xfrm_state_walk(struct xfrm_state_walk *walk,
 		    int (*func)(struct xfrm_state *, int, void*),
 		    void *data)
 {
-	struct xfrm_state *old, *x, *last = NULL;
+	struct xfrm_state *state;
+	struct xfrm_state_walk *x;
 	int err = 0;
 
-	if (walk->state == NULL && walk->count != 0)
-		return 0;
-
-	old = x = walk->state;
-	walk->state = NULL;
 	spin_lock_bh(&xfrm_state_lock);
-	if (x == NULL)
-		x = list_first_entry(&xfrm_state_all, struct xfrm_state, all);
+	if (list_empty(&walk->all))
+		x = list_first_entry(&xfrm_state_all, struct xfrm_state_walk, all);
+	else
+		x = list_entry(&walk->all, struct xfrm_state_walk, all);
 	list_for_each_entry_from(x, &xfrm_state_all, all) {
-		if (x->km.state == XFRM_STATE_DEAD)
+		if (x->state == XFRM_STATE_DEAD)
 			continue;
-		if (!xfrm_id_proto_match(x->id.proto, walk->proto))
+		state = container_of(x, struct xfrm_state, km);
+		if (!xfrm_id_proto_match(state->id.proto, walk->proto))
 			continue;
-		if (last) {
-			err = func(last, walk->count, data);
-			if (err) {
-				xfrm_state_hold(last);
-				walk->state = last;
-				goto out;
-			}
+		err = func(state, walk->seq, data);
+		if (err) {
+			list_move_tail(&walk->all, &x->all);
+			goto out;
 		}
-		last = x;
-		walk->count++;
+		walk->seq++;
 	}
-	if (walk->count == 0) {
+	if (walk->seq == 0) {
 		err = -ENOENT;
 		goto out;
 	}
-	if (last)
-		err = func(last, 0, data);
+	list_del_init(&walk->all);
 out:
 	spin_unlock_bh(&xfrm_state_lock);
-	if (old != NULL)
-		xfrm_state_put(old);
 	return err;
 }
 EXPORT_SYMBOL(xfrm_state_walk);
 
 void xfrm_state_walk_init(struct xfrm_state_walk *walk, u8 proto)
 {
+	INIT_LIST_HEAD(&walk->all);
 	walk->proto = proto;
-	walk->state = NULL;
-	walk->count = 0;
-	list_add_tail(&walk->list, &xfrm_state_walks);
-	walk->genid = ++xfrm_state_walk_ongoing;
+	walk->state = XFRM_STATE_DEAD;
+	walk->seq = 0;
 }
 EXPORT_SYMBOL(xfrm_state_walk_init);
 
 void xfrm_state_walk_done(struct xfrm_state_walk *walk)
 {
-	struct list_head *prev;
-
-	if (walk->state != NULL) {
-		xfrm_state_put(walk->state);
-		walk->state = NULL;
-	}
-
-	prev = walk->list.prev;
-	list_del(&walk->list);
-
-	if (prev != &xfrm_state_walks) {
-		list_entry(prev, struct xfrm_state_walk, list)->genid =
-			walk->genid;
+	if (list_empty(&walk->all))
 		return;
-	}
-
-	xfrm_state_walk_completed = walk->genid;
 
-	if (!list_empty(&xfrm_state_gc_leftovers))
-		schedule_work(&xfrm_state_gc_work);
+	spin_lock_bh(&xfrm_state_lock);
+	list_del(&walk->all);
+	spin_lock_bh(&xfrm_state_lock);
 }
 EXPORT_SYMBOL(xfrm_state_walk_done);