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Date: Sat, 20 Dec 2008 09:08:13 +0100
From: Gerrit Renker <gerrit@....abdn.ac.uk>
To: acme@...stprotocols.net
Cc: dccp@...r.kernel.org, netdev@...r.kernel.org
Subject: [RFC] [Patch 2/4] dccp: Lockless use of CCID blocks
dccp: Lockless use of CCIDs
This updates the implementation to use only a single array whose size
equals the number of configured CCIDs instead of 255.
Since the CCIDs are fixed array elements, synchronization is no longer
needed.
Signed-off-by: Gerrit Renker <gerrit@....abdn.ac.uk>
---
net/dccp/ccid.h | 10 ---
net/dccp/ccid.c | 166 +++++++++++---------------------------------------------
net/dccp/feat.c | 2
3 files changed, 38 insertions(+), 140 deletions(-)
--- a/net/dccp/ccid.h
+++ b/net/dccp/ccid.h
@@ -19,14 +19,12 @@
#include <linux/list.h>
#include <linux/module.h>
-#define CCID_MAX 255
-
struct tcp_info;
/**
* struct ccid_operations - Interface to Congestion-Control Infrastructure
*
- * @ccid_id: numerical CCID ID (up to %CCID_MAX, cf. table 5 in RFC 4340, 10.)
+ * @ccid_id: numerical CCID ID (cf. table 5 in RFC 4340, 10.)
* @ccid_ccmps: the CCMPS including network/transport headers (0 when disabled)
* @ccid_name: alphabetical identifier string for @ccid_id
* @ccid_hc_{r,t}x_slab: memory pool for the receiver/sender half-connection
@@ -93,9 +91,6 @@ extern struct ccid_operations ccid2_ops;
extern struct ccid_operations ccid3_ops;
#endif
-extern int ccid_register(struct ccid_operations *ccid_ops);
-extern int ccid_unregister(struct ccid_operations *ccid_ops);
-
extern int ccids_register_builtins(void);
struct ccid {
@@ -113,8 +108,7 @@ extern int ccid_get_builtin_ccids(u8 **
extern int ccid_getsockopt_builtin_ccids(struct sock *sk, int len,
char __user *, int __user *);
-extern struct ccid *ccid_new(unsigned char id, struct sock *sk, int rx,
- gfp_t gfp);
+extern struct ccid *ccid_new(const u8 id, struct sock *sk, bool rx);
static inline int ccid_get_current_rx_ccid(struct dccp_sock *dp)
{
--- a/net/dccp/ccid.c
+++ b/net/dccp/ccid.c
@@ -13,8 +13,8 @@
#include "ccid.h"
-static struct ccid_operations *builtin_ccids_ops[] = {
- &ccid2_ops, /* CCID2 is supported by default */
+static struct ccid_operations *ccids[] = {
+ &ccid2_ops, /* CCID-2 is supported by default */
#ifdef CONFIG_IP_DCCP_CCID3
&ccid3_ops,
#endif
@@ -27,49 +27,6 @@ static u8 builtin_ccids[] = {
#endif
};
-static struct ccid_operations *ccids[CCID_MAX];
-#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
-static atomic_t ccids_lockct = ATOMIC_INIT(0);
-static DEFINE_SPINLOCK(ccids_lock);
-
-/*
- * The strategy is: modifications ccids vector are short, do not sleep and
- * veeery rare, but read access should be free of any exclusive locks.
- */
-static void ccids_write_lock(void)
-{
- spin_lock(&ccids_lock);
- while (atomic_read(&ccids_lockct) != 0) {
- spin_unlock(&ccids_lock);
- yield();
- spin_lock(&ccids_lock);
- }
-}
-
-static inline void ccids_write_unlock(void)
-{
- spin_unlock(&ccids_lock);
-}
-
-static inline void ccids_read_lock(void)
-{
- atomic_inc(&ccids_lockct);
- smp_mb__after_atomic_inc();
- spin_unlock_wait(&ccids_lock);
-}
-
-static inline void ccids_read_unlock(void)
-{
- atomic_dec(&ccids_lockct);
-}
-
-#else
-#define ccids_write_lock() do { } while(0)
-#define ccids_write_unlock() do { } while(0)
-#define ccids_read_lock() do { } while(0)
-#define ccids_read_unlock() do { } while(0)
-#endif
-
static struct kmem_cache *ccid_kmem_cache_create(int obj_size, const char *fmt,...)
{
struct kmem_cache *slab;
@@ -141,56 +98,33 @@ int ccid_getsockopt_builtin_ccids(struct
return 0;
}
-int ccid_register(struct ccid_operations *ccid_ops)
+static int ccid_register(struct ccid_operations *ccid_ops)
{
- int err = -ENOBUFS;
-
ccid_ops->ccid_hc_rx_slab =
ccid_kmem_cache_create(ccid_ops->ccid_hc_rx_obj_size,
"ccid%u_hc_rx_sock",
ccid_ops->ccid_id);
if (ccid_ops->ccid_hc_rx_slab == NULL)
- goto out;
+ return -ENOBUFS;
ccid_ops->ccid_hc_tx_slab =
ccid_kmem_cache_create(ccid_ops->ccid_hc_tx_obj_size,
"ccid%u_hc_tx_sock",
ccid_ops->ccid_id);
- if (ccid_ops->ccid_hc_tx_slab == NULL)
- goto out_free_rx_slab;
- ccids_write_lock();
- err = -EEXIST;
- if (ccids[ccid_ops->ccid_id] == NULL) {
- ccids[ccid_ops->ccid_id] = ccid_ops;
- err = 0;
+ if (ccid_ops->ccid_hc_tx_slab == NULL) {
+ ccid_kmem_cache_destroy(ccid_ops->ccid_hc_rx_slab);
+ ccid_ops->ccid_hc_rx_slab = NULL;
+ return -ENOBUFS;
}
- ccids_write_unlock();
- if (err != 0)
- goto out_free_tx_slab;
pr_info("CCID: Registered CCID %d (%s)\n",
ccid_ops->ccid_id, ccid_ops->ccid_name);
-out:
- return err;
-out_free_tx_slab:
- ccid_kmem_cache_destroy(ccid_ops->ccid_hc_tx_slab);
- ccid_ops->ccid_hc_tx_slab = NULL;
- goto out;
-out_free_rx_slab:
- ccid_kmem_cache_destroy(ccid_ops->ccid_hc_rx_slab);
- ccid_ops->ccid_hc_rx_slab = NULL;
- goto out;
+ return 0;
}
-EXPORT_SYMBOL_GPL(ccid_register);
-
-int ccid_unregister(struct ccid_operations *ccid_ops)
+static int ccid_unregister(struct ccid_operations *ccid_ops)
{
- ccids_write_lock();
- ccids[ccid_ops->ccid_id] = NULL;
- ccids_write_unlock();
-
ccid_kmem_cache_destroy(ccid_ops->ccid_hc_tx_slab);
ccid_ops->ccid_hc_tx_slab = NULL;
ccid_kmem_cache_destroy(ccid_ops->ccid_hc_rx_slab);
@@ -201,14 +135,12 @@ int ccid_unregister(struct ccid_operatio
return 0;
}
-EXPORT_SYMBOL_GPL(ccid_unregister);
-
int ccids_register_builtins(void)
{
int i, err;
- for (i = 0; i < ARRAY_SIZE(builtin_ccids_ops); i++) {
- err = ccid_register(builtin_ccids_ops[i]);
+ for (i = 0; i < ARRAY_SIZE(ccids); i++) {
+ err = ccid_register(ccids[i]);
if (err)
goto unwind_registrations;
}
@@ -217,15 +149,31 @@ int ccids_register_builtins(void)
unwind_registrations:
while(--i >= 0)
- ccid_unregister(builtin_ccids_ops[i]);
+ ccid_unregister(ccids[i]);
return err;
}
-static struct ccid *__ccid_new(struct ccid_operations *ccid_ops, struct sock *sk,
- int rx, gfp_t gfp)
+
+static struct ccid_operations *ccid_find_by_id(const u8 id)
{
- struct ccid *ccid = kmem_cache_alloc(rx ? ccid_ops->ccid_hc_rx_slab :
- ccid_ops->ccid_hc_tx_slab, gfp);
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(ccids); i++)
+ if (ccids[i]->ccid_id == id)
+ return ccids[i];
+ return NULL;
+}
+
+struct ccid *ccid_new(const u8 id, struct sock *sk, bool rx)
+{
+ struct ccid_operations *ccid_ops = ccid_find_by_id(id);
+ struct ccid *ccid;
+
+ if (ccid_ops == NULL)
+ return NULL;
+
+ ccid = kmem_cache_alloc(rx ? ccid_ops->ccid_hc_rx_slab :
+ ccid_ops->ccid_hc_tx_slab, gfp_any());
if (ccid == NULL)
return NULL;
@@ -241,58 +189,14 @@ static struct ccid *__ccid_new(struct cc
ccid->ccid_ops->ccid_hc_tx_init(ccid, sk) != 0)
goto out_free_ccid;
}
+
return ccid;
+
out_free_ccid:
kmem_cache_free(rx ? ccid_ops->ccid_hc_rx_slab :
ccid_ops->ccid_hc_tx_slab, ccid);
return NULL;
}
-
-static bool is_builtin_ccid(unsigned char id)
-{
- int i;
- for (i = 0; i < ARRAY_SIZE(builtin_ccids); i++)
- if (id == builtin_ccids[i])
- return true;
- return false;
-}
-
-struct ccid *ccid_new(unsigned char id, struct sock *sk, int rx, gfp_t gfp)
-{
- struct ccid_operations *ccid_ops;
- struct ccid *ccid = NULL;
-
- if (is_builtin_ccid(id)) {
- ccid_ops = ccids[id];
- BUG_ON(ccid_ops == NULL);
- return __ccid_new(ccid_ops, sk, rx, gfp);
- }
-
- ccids_read_lock();
-#ifdef CONFIG_MODULES
- if (ccids[id] == NULL) {
- /* We only try to load if in process context */
- ccids_read_unlock();
- if (gfp & GFP_ATOMIC)
- goto out;
- request_module("net-dccp-ccid-%d", id);
- ccids_read_lock();
- }
-#endif
- ccid_ops = ccids[id];
- if (ccid_ops == NULL)
- goto out_unlock;
-
- ccids_read_unlock();
-
- ccid = __ccid_new(ccid_ops, sk, rx, gfp);
-out:
- return ccid;
-out_unlock:
- ccids_read_unlock();
- goto out;
-}
-
EXPORT_SYMBOL_GPL(ccid_new);
static void ccid_delete(struct ccid *ccid, struct sock *sk, int rx)
--- a/net/dccp/feat.c
+++ b/net/dccp/feat.c
@@ -34,7 +34,7 @@
static int dccp_hdlr_ccid(struct sock *sk, u64 ccid, bool rx)
{
struct dccp_sock *dp = dccp_sk(sk);
- struct ccid *new_ccid = ccid_new(ccid, sk, rx, gfp_any());
+ struct ccid *new_ccid = ccid_new(ccid, sk, rx);
if (new_ccid == NULL)
return -ENOMEM;
--
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