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    Subject[PATCH 5.19 147/155] ALSA: seq: Fix data-race at module auto-loading
    Date
    From: Takashi Iwai <tiwai@suse.de>

    commit 3e7e04b747adea36f349715d9f0998eeebf15d72 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    sound/core/seq/seq_clientmgr.c | 12 +++++-------
    1 file changed, 5 insertions(+), 7 deletions(-)

    --- 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_us
    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_us
    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();
    }
    }

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