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ipv4: Restore old dst_free() behavior.

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commit 404e0a8b6a (net: ipv4: fix RCU races on dst refcounts) tried
to solve a race but added a problem at device/fib dismantle time :

We really want to call dst_free() as soon as possible, even if sockets
still have dst in their cache.
dst_release() calls in free_fib_info_rcu() are not welcomed.

Root of the problem was that now we also cache output routes (in
nh_rth_output), we must use call_rcu() instead of call_rcu_bh() in
rt_free(), because output route lookups are done in process context.

Based on feedback and initial patch from David Miller (adding another
call_rcu_bh() call in fib, but it appears it was not the right fix)

I left the inet_sk_rx_dst_set() helper and added __rcu attributes
to nh_rth_output and nh_rth_input to better document what is going on in
this code.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2012-07-31 01:08:23 +00:00
committed by David S. Miller
parent 5a0d513b62
commit 54764bb647
7 changed files with 50 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/core/dst.c
+5 -21
View File
@@ -258,15 +258,6 @@ again:
}
EXPORT_SYMBOL(dst_destroy);
static void dst_rcu_destroy(struct rcu_head *head)
{
struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
dst = dst_destroy(dst);
if (dst)
__dst_free(dst);
}
void dst_release(struct dst_entry *dst)
{
if (dst) {
@@ -274,14 +265,10 @@ void dst_release(struct dst_entry *dst)
newrefcnt = atomic_dec_return(&dst->__refcnt);
WARN_ON(newrefcnt < 0);
if (unlikely(dst->flags & (DST_NOCACHE | DST_RCU_FREE)) && !newrefcnt) {
if (dst->flags & DST_RCU_FREE) {
call_rcu_bh(&dst->rcu_head, dst_rcu_destroy);
} else {
dst = dst_destroy(dst);
if (dst)
__dst_free(dst);
}
if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
dst = dst_destroy(dst);
if (dst)
__dst_free(dst);
}
}
}
@@ -333,14 +320,11 @@ EXPORT_SYMBOL(__dst_destroy_metrics_generic);
*/
void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
{
bool hold;
WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
/* If dst not in cache, we must take a reference, because
* dst_release() will destroy dst as soon as its refcount becomes zero
*/
hold = (dst->flags & (DST_NOCACHE | DST_RCU_FREE)) == DST_NOCACHE;
if (unlikely(hold)) {
if (unlikely(dst->flags & DST_NOCACHE)) {
dst_hold(dst);
skb_dst_set(skb, dst);
} else {