From 3e7e04b747adea36f349715d9f0998eeebf15d72 Mon Sep 17 00:00:00 2001

From: Takashi Iwai <tiwai@suse.de>

Date: Tue, 23 Aug 2022 09:27:17 +0200

Subject: [PATCH] ALSA: seq: Fix data-race at module auto-loading

Git-commit: 3e7e04b747adea36f349715d9f0998eeebf15d72

Patch-mainline: v6.0-rc4

References: git-fixes

It's been reported that there is a possible data-race accessing to the

global card_requested[] array at ALSA sequencer core, which is used

for determining whether to call request_module() for the card or not.

This data race itself is almost harmless, as it might end up with one

extra request_module() call for the already loaded module at most.

But it's still better to fix.

This patch addresses the possible data race of card_requested[] and

client_requested[] arrays by replacing them with bitmask.

It's an atomic operation and can work without locks.

Reported-by: Abhishek Shah <abhishek.shah@columbia.edu>

Cc: <stable@vger.kernel.org>

Link: https://lore.kernel.org/r/CAEHB24_ay6YzARpA1zgCsE7=H9CSJJzux618E=Ka4h0YdKn=qA@mail.gmail.com

Link: https://lore.kernel.org/r/20220823072717.1706-2-tiwai@suse.de

Signed-off-by: Takashi Iwai <tiwai@suse.de>

---

 sound/core/seq/seq_clientmgr.c | 12 +++++-------

 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c

index 2e9d695d336c..2d707afa1ef1 100644

--- a/sound/core/seq/seq_clientmgr.c

+++ b/sound/core/seq/seq_clientmgr.c

@@ -121,13 +121,13 @@ struct snd_seq_client *snd_seq_client_use_ptr(int clientid)

 	spin_unlock_irqrestore(&clients_lock, flags);

 #ifdef CONFIG_MODULES

 	if (!in_interrupt()) {

-		static char client_requested[SNDRV_SEQ_GLOBAL_CLIENTS];

-		static char card_requested[SNDRV_CARDS];

+		static DECLARE_BITMAP(client_requested, SNDRV_SEQ_GLOBAL_CLIENTS);

+		static DECLARE_BITMAP(card_requested, SNDRV_CARDS);

+

 		if (clientid < SNDRV_SEQ_GLOBAL_CLIENTS) {

 			int idx;

-			if (!client_requested[clientid]) {

-				client_requested[clientid] = 1;

+			if (!test_and_set_bit(clientid, client_requested)) {

 				for (idx = 0; idx < 15; idx++) {

 					if (seq_client_load[idx] < 0)

 						break;

@@ -142,10 +142,8 @@ struct snd_seq_client *snd_seq_client_use_ptr(int clientid)

 			int card = (clientid - SNDRV_SEQ_GLOBAL_CLIENTS) /

 				SNDRV_SEQ_CLIENTS_PER_CARD;

 			if (card < snd_ecards_limit) {

-				if (! card_requested[card]) {

-					card_requested[card] = 1;

+				if (!test_and_set_bit(card, card_requested))

 					snd_request_card(card);

-				}

 				snd_seq_device_load_drivers();

 			}

 		}

-- 

2.35.3