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Message-ID: <48D88BCC.5030806@iki.fi>
Date: Tue, 23 Sep 2008 09:25:16 +0300
From: Timo Teräs <timo.teras@....fi>
To: Herbert Xu <herbert@...dor.apana.org.au>
CC: David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: xfrm_state locking regression...
Herbert Xu wrote:
> On Tue, Sep 23, 2008 at 08:17:14AM +0300, Timo Teräs wrote:
>> The extra step there wold be a hold call. The recursive _put on a
>> _put of some entry can happen only on dump path. As otherwise the
>> ->next entry is first held in state delete, but would be immediately
>> _put on the _put as the final step of _delete().
>>
>> So basically one additional atomic_inc() and one atomic_dec() on the
>> normal _delete() path.
>
> Can you post a patch? If this can be done locklessly then yes
> it would probably be a good way to go. However, I'm not sure
> whether I understand your lockless proposal yet.
Something like this. I just compile tested, so I'm not sure if it
actually works.
This basically reverts the GC changes. The interesting bits are in
xfrm_state_delete(). It will _hold() the ->next entry unless we
were at last entry. This will make sure that when an entry is
in XFRM_STATE_DEAD the all.next is valid all the way until the
entry is destroyed.
The corresponding put is in _destroy(). Added it as a final thing
to do so hopefully compiler optimizes tail recursion to iteration.
(Seemed to do that in my case.)
And finally, _walk() was right all along. It returns to dumping
and first skips all dead entries. And just before return, when
all dead entries are already skipped the originally held entry
is _put(). That _put call (or the one in _walk_done()) will result
all dead entries that were held, to be iteratively put.
- Timo
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..d5cba7b 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -122,7 +122,7 @@ struct xfrm_state
{
struct list_head all;
union {
- struct list_head gclist;
+ struct hlist_node gclist;
struct hlist_node bydst;
};
struct hlist_node bysrc;
@@ -1246,8 +1246,6 @@ struct xfrm6_tunnel {
};
struct xfrm_state_walk {
- struct list_head list;
- unsigned long genid;
struct xfrm_state *state;
int count;
u8 proto;
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 053970e..f45f006 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 +403,17 @@ 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);
+ gc_list.first = xfrm_state_gc_list.first;
+ INIT_HLIST_HEAD(&xfrm_state_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);
}
@@ -553,12 +538,19 @@ EXPORT_SYMBOL(xfrm_state_alloc);
void __xfrm_state_destroy(struct xfrm_state *x)
{
+ struct xfrm_state *next = NULL;
+
WARN_ON(x->km.state != XFRM_STATE_DEAD);
+ if (x->all.next != &xfrm_state_all)
+ next = container_of(x->all.next, struct xfrm_state, all);
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);
+
+ if (next != NULL)
+ xfrm_state_put(next);
}
EXPORT_SYMBOL(__xfrm_state_destroy);
@@ -569,8 +561,10 @@ 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);
+ if (x->all.next != &xfrm_state_all)
+ xfrm_state_hold(container_of(x->all.next,
+ struct xfrm_state, all));
hlist_del(&x->bydst);
hlist_del(&x->bysrc);
if (x->id.spi)
@@ -1612,33 +1606,15 @@ void xfrm_state_walk_init(struct xfrm_state_walk *walk, u8 proto)
walk->proto = proto;
walk->state = NULL;
walk->count = 0;
- list_add_tail(&walk->list, &xfrm_state_walks);
- walk->genid = ++xfrm_state_walk_ongoing;
}
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;
- return;
- }
-
- xfrm_state_walk_completed = walk->genid;
-
- if (!list_empty(&xfrm_state_gc_leftovers))
- schedule_work(&xfrm_state_gc_work);
}
EXPORT_SYMBOL(xfrm_state_walk_done);
--
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