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ALSA: seq: Wait for one RCU grace period when deleting all ports

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Since the port list was converted to RCU, snd_seq_delete_all_ports()
calls synchronize_rcu() once per port under register_mutex. Closing a
client with 254 ports now takes about 1.6s and every other client
open or close waits for it.

Unlink all ports first, wait for a single grace period and then free
them.

Fixes: 4c252fbc06 ("ALSA: seq: Use RCU for the client port list")
Signed-off-by: Ali Ahmet Memiş <aliamemis@disroot.org>
Link: https://patch.msgid.link/20261010222543.1470723-1-aliamemis@disroot.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Ali Ahmet Memiş 2026-10-11 01:25:40 +03:00 committed by Takashi Iwai
parent 947037990e
commit 7ca1731b8a
2 changed files with 28 additions and 14 deletions
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41
sound/core/seq/seq_ports.c
View File

@ -248,17 +248,9 @@ static void clear_subscriber_list(struct snd_seq_client *client,
}
/* delete port data */
static int port_delete(struct snd_seq_client *client,
struct snd_seq_client_port *port)
static void port_free(struct snd_seq_client *client,
struct snd_seq_client_port *port)
{
/* set closing flag and wait for all port access are gone */
port->closing = 1;
/* the port has already been unlinked from the client's port list;
* wait for a grace period so that RCU readers still traversing the
* list can no longer take a new use_lock reference, then drain the
* outstanding references before freeing
*/
synchronize_rcu();
snd_use_lock_sync(&port->use_lock);
/* clear subscribers info */
@ -272,6 +264,20 @@ static int port_delete(struct snd_seq_client *client,
snd_BUG_ON(port->c_dest.count != 0);
kfree(port);
}
static int port_delete(struct snd_seq_client *client,
struct snd_seq_client_port *port)
{
/* set closing flag and wait for all port access are gone */
port->closing = 1;
/* the port has already been unlinked from the client's port list;
* wait for a grace period so that RCU readers still traversing the
* list can no longer take a new use_lock reference, then drain the
* outstanding references before freeing
*/
synchronize_rcu();
port_free(client, port);
return 0;
}
@ -302,18 +308,25 @@ int snd_seq_delete_port(struct snd_seq_client *client, int port)
int snd_seq_delete_all_ports(struct snd_seq_client *client)
{
struct snd_seq_client_port *port, *tmp;
LIST_HEAD(deleted);
/* unlink and delete each port; port_delete() waits for an RCU grace
* period before draining the port, so concurrent lockless readers can
* no longer take a new use_lock reference on it
/* unlink all ports first and wait for a single RCU grace period
* before draining and freeing them, so concurrent lockless readers
* can no longer take a new use_lock reference on any of them
*/
guard(mutex)(&client->ports_mutex);
list_for_each_entry_safe(port, tmp, &client->ports_list_head, list) {
list_del_rcu(&port->list);
client->num_ports--;
port->closing = 1;
list_add_tail(&port->delete_list, &deleted);
snd_seq_system_client_ev_port_exit(port->addr.client, port->addr.port);
port_delete(client, port);
}
if (list_empty(&deleted))
return 0;
synchronize_rcu();
list_for_each_entry_safe(port, tmp, &deleted, delete_list)
port_free(client, port);
return 0;
}

1
sound/core/seq/seq_ports.h
View File

@ -49,6 +49,7 @@ struct snd_seq_client_port {
struct module *owner; /* owner of this port */
char name[64]; /* port name */
struct list_head list; /* port list */
struct list_head delete_list; /* used by snd_seq_delete_all_ports() */
snd_use_lock_t use_lock;
/* subscribers */