[bug report] ALSA: usb-audio: qcom: Introduce QC USB SND offloading support

[Dan Carpenter <dan.carpenter@linaro.org>]

Hello Wesley Cheng,

Commit 326bbc348298 ("ALSA: usb-audio: qcom: Introduce QC USB SND
offloading support") from Apr 9, 2025 (linux-next), leads to the
following Smatch static checker warning:

	sound/usb/qcom/qc_audio_offload.c:762 qmi_stop_session()
	error: we previously assumed 'subs' could be null (see line 761)

sound/usb/qcom/qc_audio_offload.c
    737 static void qmi_stop_session(void)
    738 {
    739         struct snd_usb_substream *subs;
    740         struct usb_host_endpoint *ep;
    741         struct snd_usb_audio *chip;
    742         struct intf_info *info;
    743         int pcm_card_num;
    744         int if_idx;
    745         int idx;
    746 
    747         mutex_lock(&qdev_mutex);
    748         /* find all active intf for set alt 0 and cleanup usb audio dev */
    749         for (idx = 0; idx < SNDRV_CARDS; idx++) {
    750                 if (!atomic_read(&uadev[idx].in_use))
    751                         continue;
    752 
    753                 chip = uadev[idx].chip;
    754                 for (if_idx = 0; if_idx < uadev[idx].num_intf; if_idx++) {
    755                         if (!uadev[idx].info || !uadev[idx].info[if_idx].in_use)
    756                                 continue;
    757                         info = &uadev[idx].info[if_idx];
    758                         pcm_card_num = info->pcm_card_num;
    759                         subs = find_substream(pcm_card_num, info->pcm_dev_num,
    760                                               info->direction);
    761                         if (!subs || !chip || atomic_read(&chip->shutdown)) {
                                     ^^^^
Check for NULL

--> 762                                 dev_err(&subs->dev->dev,
                                                ^^^^^^^^^^^^^^^
Unchecked derefrence

    763                                         "no sub for c#%u dev#%u dir%u\n",
    764                                         info->pcm_card_num,
    765                                         info->pcm_dev_num,
    766                                         info->direction);
    767                                 continue;

regards,
dan carpenter