Currently, use_count is used in snd_usb_endpoint_set_params to ensure the parameters don't get changed for an in-use endpoint.
However, there is a subtle condition where this check fails - if hw_params is called on both substreams before calling prepare (for playback) or start trigger (for capture): the endpoint is not yet started, i.e., snd_usb_endpoint_start() does not yet increment use_count.
This adds a flag to check if the parameters are set, but does not omit checking the use_count.
Signed-off-by: Eldad Zack eldad@fogrefinery.com --- sound/usb/card.h | 1 + sound/usb/endpoint.c | 11 ++++++++--- 2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/sound/usb/card.h b/sound/usb/card.h index 5ecacaa..4061ee1 100644 --- a/sound/usb/card.h +++ b/sound/usb/card.h @@ -51,6 +51,7 @@ struct snd_usb_endpoint { struct snd_usb_audio *chip;
int use_count; + bool param_set; int ep_num; /* the referenced endpoint number */ int type; /* SND_USB_ENDPOINT_TYPE_* */ unsigned long flags; diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c index 4241154..a56e769 100644 --- a/sound/usb/endpoint.c +++ b/sound/usb/endpoint.c @@ -469,6 +469,8 @@ struct snd_usb_endpoint *snd_usb_add_endpoint(struct snd_usb_audio *chip, ep->syncmaxsize = le16_to_cpu(get_endpoint(alts, 1)->wMaxPacketSize); }
+ ep->param_set = false; + list_add_tail(&ep->list, &chip->ep_list);
__exit_unlock: @@ -792,13 +794,15 @@ int snd_usb_endpoint_set_params(struct snd_usb_endpoint *ep, { int err;
- if ((!subs && ep->use_count != 0) || - !snd_usb_endpoint_may_set_params(subs, pcm_format, channels, - period_bytes, rate)) { + if (ep->param_set && + ((!subs && ep->use_count != 0) || + !snd_usb_endpoint_may_set_params(subs, pcm_format, channels, + period_bytes, rate))) { snd_printk(KERN_WARNING "Unable to change format on ep #%x: already in use\n", ep->ep_num); return -EBUSY; } + ep->param_set = true;
/* release old buffers, if any */ release_urbs(ep, 0); @@ -950,6 +954,7 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep) ep->sync_slave = NULL; ep->retire_data_urb = NULL; ep->prepare_data_urb = NULL; + ep->param_set = false; set_bit(EP_FLAG_STOPPING, &ep->flags); } }