linux-kernel - [PATCH 3.16 343/410] ALSA: seq: Clear client entry before deleting else at closing

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Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.16 343/410] ALSA: seq: Clear client entry before
 deleting else at closing

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

commit a2ff19f7b70118ced291a28d5313469914de451b upstream.

When releasing a client, we need to clear the clienttab[] entry at
first, then call snd_seq_queue_client_leave().  Otherwise, the
in-flight cell in the queue might be picked up by the timer interrupt
via snd_seq_check_queue() before calling snd_seq_queue_client_leave(),
and it's delivered to another queue while the client is clearing
queues.  This may eventually result in an uncleared cell remaining in
a queue, and the later snd_seq_pool_delete() may need to wait for a
long time until the event gets really processed.

By moving the clienttab[] clearance at the beginning of release, any
event delivery of a cell belonging to this client will fail at a later
point, since snd_seq_client_ptr() returns NULL.  Thus the cell that
was picked up by the timer interrupt will be returned immediately
without further delivery, and the long stall of snd_seq_delete_pool()
can be avoided, too.

Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 sound/core/seq/seq_clientmgr.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -270,12 +270,12 @@ static int seq_free_client1(struct snd_s

 	if (!client)
 		return 0;
-	snd_seq_delete_all_ports(client);
-	snd_seq_queue_client_leave(client->number);
 	spin_lock_irqsave(&clients_lock, flags);
 	clienttablock[client->number] = 1;
 	clienttab[client->number] = NULL;
 	spin_unlock_irqrestore(&clients_lock, flags);
+	snd_seq_delete_all_ports(client);
+	snd_seq_queue_client_leave(client->number);
 	snd_use_lock_sync(&client->use_lock);
 	snd_seq_queue_client_termination(client->number);
 	if (client->pool)