[PATCH 5.15 605/917] ALSA: usb-audio: Fix possible race at sync of urb completions
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2021-11-15 23:51:20
Also in:
lkml
Subsystem:
sound, the rest · Maintainers:
Jaroslav Kysela, Takashi Iwai, Linus Torvalds
From: Takashi Iwai <redacted> [ Upstream commit 86a42ad07905110f82648853c0ea3434b4eab173 ] 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 (local) Signed-off-by: Takashi Iwai <redacted> Signed-off-by: Sasha Levin <sashal@kernel.org> --- sound/usb/card.h | 1 + sound/usb/endpoint.c | 7 ++++++- 2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/sound/usb/card.h b/sound/usb/card.h
index 5b19901f305a3..860faaf249ea6 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 */
diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 533919a28856f..ba2d7e6884207 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c@@ -451,6 +451,7 @@ static void queue_pending_output_urbs(struct snd_usb_endpoint *ep) } set_bit(ctx->index, &ep->active_mask); + atomic_inc(&ep->submitted_urbs); } }
@@ -488,6 +489,7 @@ static void snd_complete_urb(struct urb *urb) clear_bit(ctx->index, &ep->active_mask); spin_unlock_irqrestore(&ep->lock, flags); queue_pending_output_urbs(ep); + atomic_dec(&ep->submitted_urbs); /* decrement at last */ return; }
@@ -513,6 +515,7 @@ static void snd_complete_urb(struct urb *urb) exit_clear: clear_bit(ctx->index, &ep->active_mask); + atomic_dec(&ep->submitted_urbs); } /*
@@ -596,6 +599,7 @@ int snd_usb_add_endpoint(struct snd_usb_audio *chip, int ep_num, int type) ep->type = type; ep->ep_num = ep_num; INIT_LIST_HEAD(&ep->ready_playback_urbs); + atomic_set(&ep->submitted_urbs, 0); is_playback = ((ep_num & USB_ENDPOINT_DIR_MASK) == USB_DIR_OUT); ep_num &= USB_ENDPOINT_NUMBER_MASK;
@@ -859,7 +863,7 @@ static int wait_clear_urbs(struct snd_usb_endpoint *ep) return 0; do { - alive = bitmap_weight(&ep->active_mask, ep->nurbs); + alive = atomic_read(&ep->submitted_urbs); if (!alive) break;
@@ -1420,6 +1424,7 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep) goto __error; } set_bit(i, &ep->active_mask); + atomic_inc(&ep->submitted_urbs); } usb_audio_dbg(ep->chip, "%d URBs submitted for EP 0x%x\n",
--
2.33.0