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>
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 @@
#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 @@
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 @@
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;