From 86a42ad07905110f82648853c0ea3434b4eab173 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Wed, 29 Sep 2021 10:08:37 +0200 Subject: ALSA: usb-audio: Fix possible race at sync of urb completions USB-audio driver tries to sync with the clear of all pending URBs in wait_clear_urbs(), and it waits for all bits in active_mask getting cleared. This works fine for the normal operations, but when a stream is managed in the implicit feedback mode, there is still a very thin race window: namely, in snd_complete_usb(), the active_mask bit for the current URB is once cleared before re-submitted in queue_pending_output_urbs(). If wait_clear_urbs() is called during that period, it may pass the test and go forward even though there may be a still pending URB. For covering it, this patch adds a new counter to each endpoint to keep the number of in-flight URBs, and changes wait_clear_urbs() checking this number instead. The counter is decremented at the end of URB complete, hence the reference is kept as long as the URB complete is in process. Link: https://lore.kernel.org/r/20210929080844.11583-3-tiwai@suse.de Signed-off-by: Takashi Iwai --- sound/usb/card.h | 1 + 1 file changed, 1 insertion(+) (limited to 'sound/usb/card.h') diff --git a/sound/usb/card.h b/sound/usb/card.h index 3329ce710cb9..746a765b2437 100644 --- a/sound/usb/card.h +++ b/sound/usb/card.h @@ -97,6 +97,7 @@ struct snd_usb_endpoint { unsigned int nominal_queue_size; /* total buffer sizes in URBs */ unsigned long active_mask; /* bitmask of active urbs */ unsigned long unlink_mask; /* bitmask of unlinked urbs */ + atomic_t submitted_urbs; /* currently submitted urbs */ char *syncbuf; /* sync buffer for all sync URBs */ dma_addr_t sync_dma; /* DMA address of syncbuf */ -- cgit 1.4.1