net: sock_def_readable() and friends RCU conversion

sk_callback_lock rwlock actually protects sk->sk_sleep pointer, so we
need two atomic operations (and associated dirtying) per incoming
packet.

RCU conversion is pretty much needed :

1) Add a new structure, called "struct socket_wq" to hold all fields
that will need rcu_read_lock() protection (currently: a
wait_queue_head_t and a struct fasync_struct pointer).

[Future patch will add a list anchor for wakeup coalescing]

2) Attach one of such structure to each "struct socket" created in
sock_alloc_inode().

3) Respect RCU grace period when freeing a "struct socket_wq"

4) Change sk_sleep pointer in "struct sock" by sk_wq, pointer to "struct
socket_wq"

5) Change sk_sleep() function to use new sk->sk_wq instead of
sk->sk_sleep

6) Change sk_has_sleeper() to wq_has_sleeper() that must be used inside
a rcu_read_lock() section.

7) Change all sk_has_sleeper() callers to :
  - Use rcu_read_lock() instead of read_lock(&sk->sk_callback_lock)
  - Use wq_has_sleeper() to eventually wakeup tasks.
  - Use rcu_read_unlock() instead of read_unlock(&sk->sk_callback_lock)

8) sock_wake_async() is modified to use rcu protection as well.

9) Exceptions :
  macvtap, drivers/net/tun.c, af_unix use integrated "struct socket_wq"
instead of dynamically allocated ones. They dont need rcu freeing.

Some cleanups or followups are probably needed, (possible
sk_callback_lock conversion to a spinlock for example...).

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 5 deletions

diff --git a/include/linux/net.h b/include/linux/net.h
index 4157b5d..2b4deee 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -59,6 +59,7 @@ typedef enum {
 #include <linux/wait.h>
 #include <linux/fcntl.h>	/* For O_CLOEXEC and O_NONBLOCK */
 #include <linux/kmemcheck.h>
+#include <linux/rcupdate.h>
 
 struct poll_table_struct;
 struct pipe_inode_info;
@@ -116,6 +117,12 @@ enum sock_shutdown_cmd {
 	SHUT_RDWR	= 2,
 };
 
+struct socket_wq {
+	wait_queue_head_t	wait;
+	struct fasync_struct	*fasync_list;
+	struct rcu_head		rcu;
+} ____cacheline_aligned_in_smp;
+
 /**
  *  struct socket - general BSD socket
  *  @state: socket state (%SS_CONNECTED, etc)
@@ -135,11 +142,8 @@ struct socket {
 	kmemcheck_bitfield_end(type);
 
 	unsigned long		flags;
-	/*
-	 * Please keep fasync_list & wait fields in the same cache line
-	 */
-	struct fasync_struct	*fasync_list;
-	wait_queue_head_t	wait;
+
+	struct socket_wq	*wq;
 
 	struct file		*file;
 	struct sock		*sk;