[INET]: Generalise the tcp_listen_ lock routines
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 33d6cbe..06cbc6f 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -15,7 +15,9 @@
#include <linux/config.h>
#include <linux/module.h>
+#include <linux/sched.h>
#include <linux/slab.h>
+#include <linux/wait.h>
#include <net/inet_hashtables.h>
@@ -89,3 +91,33 @@
}
EXPORT_SYMBOL(inet_put_port);
+
+/*
+ * This lock without WQ_FLAG_EXCLUSIVE is good on UP and it can be very bad on SMP.
+ * Look, when several writers sleep and reader wakes them up, all but one
+ * immediately hit write lock and grab all the cpus. Exclusive sleep solves
+ * this, _but_ remember, it adds useless work on UP machines (wake up each
+ * exclusive lock release). It should be ifdefed really.
+ */
+void inet_listen_wlock(struct inet_hashinfo *hashinfo)
+{
+ write_lock(&hashinfo->lhash_lock);
+
+ if (atomic_read(&hashinfo->lhash_users)) {
+ DEFINE_WAIT(wait);
+
+ for (;;) {
+ prepare_to_wait_exclusive(&hashinfo->lhash_wait,
+ &wait, TASK_UNINTERRUPTIBLE);
+ if (!atomic_read(&hashinfo->lhash_users))
+ break;
+ write_unlock_bh(&hashinfo->lhash_lock);
+ schedule();
+ write_lock_bh(&hashinfo->lhash_lock);
+ }
+
+ finish_wait(&hashinfo->lhash_wait, &wait);
+ }
+}
+
+EXPORT_SYMBOL(inet_listen_wlock);