[Cluster-devel] [PATCH dlm/next 2/7] fs: dlm: make connection hash lockless
Alexander Aring
aahringo at redhat.com
Thu Aug 27 19:02:49 UTC 2020
There are some problems with the connections_lock. During my
experiements I saw sometimes circular dependencies with sock_lock.
The reason here might be code parts which runs nodeid2con() before
or after sock_lock is acquired.
Another issue are missing locks in for_conn() iteration. Maybe this
works fine because for_conn() is running in a context where
connection_hash cannot be manipulated by others anymore.
However this patch changes the connection_hash to be protected by
sleepable rcu. The hotpath function __find_con() is implemented
lockless as it is only a reader of connection_hash and this hopefully
fixes the circular locking dependencies. The iteration for_conn() will
still call some sleepable functionality, that's why we use sleepable rcu
in this case.
This patch removes the kmemcache functionality as I think I need to
make some free() functionality via call_rcu(). However allocation time
isn't here an issue. The dlm_allow_con will not be protected by a lock
anymore as I think it's enough to just set and flush workqueues
afterwards.
Signed-off-by: Alexander Aring <aahringo at redhat.com>
---
fs/dlm/Kconfig | 1 +
fs/dlm/lowcomms.c | 86 ++++++++++++++++++++---------------------------
2 files changed, 37 insertions(+), 50 deletions(-)
diff --git a/fs/dlm/Kconfig b/fs/dlm/Kconfig
index f82a4952769d..ee92634196a8 100644
--- a/fs/dlm/Kconfig
+++ b/fs/dlm/Kconfig
@@ -4,6 +4,7 @@ menuconfig DLM
depends on INET
depends on SYSFS && CONFIGFS_FS && (IPV6 || IPV6=n)
select IP_SCTP
+ select SRCU
help
A general purpose distributed lock manager for kernel or userspace
applications.
diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index ed098870ba0d..9db7126de793 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -126,6 +126,7 @@ struct connection {
struct work_struct rwork; /* Receive workqueue */
struct work_struct swork; /* Send workqueue */
wait_queue_head_t shutdown_wait; /* wait for graceful shutdown */
+ struct rcu_head rcu;
};
#define sock2con(x) ((struct connection *)(x)->sk_user_data)
@@ -167,8 +168,8 @@ static struct workqueue_struct *recv_workqueue;
static struct workqueue_struct *send_workqueue;
static struct hlist_head connection_hash[CONN_HASH_SIZE];
-static DEFINE_MUTEX(connections_lock);
-static struct kmem_cache *con_cache;
+static DEFINE_SPINLOCK(connections_lock);
+DEFINE_STATIC_SRCU(connections_srcu);
static void process_recv_sockets(struct work_struct *work);
static void process_send_sockets(struct work_struct *work);
@@ -184,15 +185,20 @@ static inline int nodeid_hash(int nodeid)
static struct connection *__find_con(int nodeid)
{
- int r;
+ int r, idx;
struct connection *con;
r = nodeid_hash(nodeid);
- hlist_for_each_entry(con, &connection_hash[r], list) {
- if (con->nodeid == nodeid)
+ idx = srcu_read_lock(&connections_srcu);
+ hlist_for_each_entry_rcu(con, &connection_hash[r], list) {
+ if (con->nodeid == nodeid) {
+ srcu_read_unlock(&connections_srcu, idx);
return con;
+ }
}
+ srcu_read_unlock(&connections_srcu, idx);
+
return NULL;
}
@@ -200,7 +206,7 @@ static struct connection *__find_con(int nodeid)
* If 'allocation' is zero then we don't attempt to create a new
* connection structure for this node.
*/
-static struct connection *__nodeid2con(int nodeid, gfp_t alloc)
+static struct connection *nodeid2con(int nodeid, gfp_t alloc)
{
struct connection *con = NULL;
int r;
@@ -209,13 +215,10 @@ static struct connection *__nodeid2con(int nodeid, gfp_t alloc)
if (con || !alloc)
return con;
- con = kmem_cache_zalloc(con_cache, alloc);
+ con = kzalloc(sizeof(*con), alloc);
if (!con)
return NULL;
- r = nodeid_hash(nodeid);
- hlist_add_head(&con->list, &connection_hash[r]);
-
con->nodeid = nodeid;
mutex_init(&con->sock_mutex);
INIT_LIST_HEAD(&con->writequeue);
@@ -233,31 +236,27 @@ static struct connection *__nodeid2con(int nodeid, gfp_t alloc)
con->rx_action = zerocon->rx_action;
}
+ r = nodeid_hash(nodeid);
+
+ spin_lock(&connections_lock);
+ hlist_add_head_rcu(&con->list, &connection_hash[r]);
+ spin_unlock(&connections_lock);
+
return con;
}
/* Loop round all connections */
static void foreach_conn(void (*conn_func)(struct connection *c))
{
- int i;
- struct hlist_node *n;
+ int i, idx;
struct connection *con;
+ idx = srcu_read_lock(&connections_srcu);
for (i = 0; i < CONN_HASH_SIZE; i++) {
- hlist_for_each_entry_safe(con, n, &connection_hash[i], list)
+ hlist_for_each_entry_rcu(con, &connection_hash[i], list)
conn_func(con);
}
-}
-
-static struct connection *nodeid2con(int nodeid, gfp_t allocation)
-{
- struct connection *con;
-
- mutex_lock(&connections_lock);
- con = __nodeid2con(nodeid, allocation);
- mutex_unlock(&connections_lock);
-
- return con;
+ srcu_read_unlock(&connections_srcu, idx);
}
static struct dlm_node_addr *find_node_addr(int nodeid)
@@ -792,12 +791,9 @@ static int accept_from_sock(struct connection *con)
struct connection *newcon;
struct connection *addcon;
- mutex_lock(&connections_lock);
if (!dlm_allow_conn) {
- mutex_unlock(&connections_lock);
return -1;
}
- mutex_unlock(&connections_lock);
mutex_lock_nested(&con->sock_mutex, 0);
@@ -847,7 +843,7 @@ static int accept_from_sock(struct connection *con)
struct connection *othercon = newcon->othercon;
if (!othercon) {
- othercon = kmem_cache_zalloc(con_cache, GFP_NOFS);
+ othercon = kzalloc(sizeof(*othercon), GFP_NOFS);
if (!othercon) {
log_print("failed to allocate incoming socket");
mutex_unlock(&newcon->sock_mutex);
@@ -1612,16 +1608,17 @@ static void free_conn(struct connection *con)
{
close_connection(con, true, true, true);
if (con->othercon)
- kmem_cache_free(con_cache, con->othercon);
- hlist_del(&con->list);
- kmem_cache_free(con_cache, con);
+ kfree_rcu(con->othercon, rcu);
+ spin_lock(&connections_lock);
+ hlist_del_rcu(&con->list);
+ spin_unlock(&connections_lock);
+ kfree_rcu(con, rcu);
}
static void work_flush(void)
{
- int ok;
+ int ok, idx;
int i;
- struct hlist_node *n;
struct connection *con;
do {
@@ -1631,9 +1628,10 @@ static void work_flush(void)
flush_workqueue(recv_workqueue);
if (send_workqueue)
flush_workqueue(send_workqueue);
+ idx = srcu_read_lock(&connections_srcu);
for (i = 0; i < CONN_HASH_SIZE && ok; i++) {
- hlist_for_each_entry_safe(con, n,
- &connection_hash[i], list) {
+ hlist_for_each_entry_rcu(con, &connection_hash[i],
+ list) {
ok &= test_bit(CF_READ_PENDING, &con->flags);
ok &= test_bit(CF_WRITE_PENDING, &con->flags);
if (con->othercon) {
@@ -1644,6 +1642,7 @@ static void work_flush(void)
}
}
}
+ srcu_read_unlock(&connections_srcu, idx);
} while (!ok);
}
@@ -1652,9 +1651,7 @@ void dlm_lowcomms_stop(void)
/* Set all the flags to prevent any
socket activity.
*/
- mutex_lock(&connections_lock);
dlm_allow_conn = 0;
- mutex_unlock(&connections_lock);
if (recv_workqueue)
flush_workqueue(recv_workqueue);
@@ -1666,8 +1663,6 @@ void dlm_lowcomms_stop(void)
clean_writequeues();
foreach_conn(free_conn);
work_stop();
-
- kmem_cache_destroy(con_cache);
}
int dlm_lowcomms_start(void)
@@ -1686,16 +1681,9 @@ int dlm_lowcomms_start(void)
goto fail;
}
- error = -ENOMEM;
- con_cache = kmem_cache_create("dlm_conn", sizeof(struct connection),
- __alignof__(struct connection), 0,
- NULL);
- if (!con_cache)
- goto fail;
-
error = work_start();
if (error)
- goto fail_destroy;
+ goto fail;
dlm_allow_conn = 1;
@@ -1714,10 +1702,8 @@ int dlm_lowcomms_start(void)
con = nodeid2con(0,0);
if (con) {
close_connection(con, false, true, true);
- kmem_cache_free(con_cache, con);
+ kfree_rcu(con, rcu);
}
-fail_destroy:
- kmem_cache_destroy(con_cache);
fail:
return error;
}
--
2.26.2
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