We have tested this patch and confirm it eliminates the race we initially reported. Best, Gabe On Tue, Aug 23, 2022 at 3:27 AM Takashi Iwai <tiwai@xxxxxxx> 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@xxxxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Link: > https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_r_CAEHB24-5Fay6YzARpA1zgCsE7-3DH9CSJJzux618E-3DKa4h0YdKn-3DqA-40mail.gmail.com&d=DwIDAg&c=009klHSCxuh5AI1vNQzSO0KGjl4nbi2Q0M1QLJX9BeE&r=EyAJYRJu01oaAhhVVY3o8zKgZvacDAXd_PNRtaqACCo&m=oPAvNa2pfJuUIAiwbiE1IJgoQhWb8AB7IBdJqWslhhuZ-LwBrrgAnFUthdapQska&s=K26ukWoQce9A8OzoQEGfRXynlOouHQ79dnAnD7xriNw&e= > > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> > --- > 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..052a690b5e11 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_requested, > card)) > snd_request_card(card); > - } > snd_seq_device_load_drivers(); > } > } > -- > 2.35.3 > >
