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fs: dlm: make connection hash lockless 

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@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>
This commit is contained in:
Alexander Aring 2020-08-27 15:02:49 -04:00 committed by David Teigland
parent aa7ab1e208
commit a47666eb76
2 changed files with 37 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
fs/dlm/Kconfig
View File

@ -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.

86
fs/dlm/lowcomms.c
View File

@ -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;
}