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ALSA: seq: Fix data-race at module auto-loading 

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>
This commit is contained in:
Takashi Iwai 2022-08-23 09:27:17 +02:00
parent 22dec134db
commit 3e7e04b747
1 changed files with 5 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
sound/core/seq/seq_clientmgr.c
View File

@ -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();
}
}