l2tp: avoid deadlock in l2tp stats update
l2tp's u64_stats writers were incorrectly synchronised, making it possible to
deadlock a 64bit machine running a 32bit kernel simply by sending the l2tp
code netlink commands while passing data through l2tp sessions.
Previous discussion on netdev determined that alternative solutions such as
spinlock writer synchronisation or per-cpu data would bring unjustified
overhead, given that most users interested in high volume traffic will likely
be running 64bit kernels on 64bit hardware.
As such, this patch replaces l2tp's use of u64_stats with atomic_long_t,
thereby avoiding the deadlock.
Ref:
http://marc.info/?l=linux-netdev&m=134029167910731&w=2
http://marc.info/?l=linux-netdev&m=134079868111131&w=2
Signed-off-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index d40713d..519b013 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -36,16 +36,15 @@
struct sk_buff;
struct l2tp_stats {
- u64 tx_packets;
- u64 tx_bytes;
- u64 tx_errors;
- u64 rx_packets;
- u64 rx_bytes;
- u64 rx_seq_discards;
- u64 rx_oos_packets;
- u64 rx_errors;
- u64 rx_cookie_discards;
- struct u64_stats_sync syncp;
+ atomic_long_t tx_packets;
+ atomic_long_t tx_bytes;
+ atomic_long_t tx_errors;
+ atomic_long_t rx_packets;
+ atomic_long_t rx_bytes;
+ atomic_long_t rx_seq_discards;
+ atomic_long_t rx_oos_packets;
+ atomic_long_t rx_errors;
+ atomic_long_t rx_cookie_discards;
};
struct l2tp_tunnel;