Apologies, I just realized the previous patch raised incompatible integer conversion warnings on that line during compilation. In the future I'll keep a closer eye out for relevant warnings when testing.
This patch still eliminates the race we initially reported.
Best,
Gabe
On Wed, Aug 24, 2022 at 2:03 AM Takashi Iwai tiwai@suse.de wrote:
On Tue, 23 Aug 2022 09:27:17 +0200, Takashi Iwai wrote:
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://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_r_CAEHB... Signed-off-by: Takashi Iwai tiwai@suse.de
Gah, there was an obvious type in the patch. The correct version is below, and I merged it now.
thanks,
Takashi
-- 8< -- From: Takashi Iwai tiwai@suse.de Subject: [PATCH v2] 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://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_r_CAEHB... Link: https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_r_20220... Signed-off-by: Takashi Iwai tiwai@suse.de
v1->v2: fix compile error
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