ALSA: usb-audio: Fix racy list management in output queue (5b6cc38f) · Commits · 戴 / test

The linked list entry from FIFO is peeked at queue_pending_output_urbs() but the actual element pop-out is performed outside the spinlock, and it's potentially racy. Do delete the link at the right place inside the spinlock. Fixes: ("ALSA: snd-usb: implement new endpoint streaming model") Link: https://lore.kernel.org/r/20200424074016.14301-1-tiwai@suse.de Signed-off-by:

Takashi Iwai <tiwai@suse.de>

sound/usb/endpoint.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -346,17 +346,17 @@ static void queue_pending_output_urbs(struct snd_usb_endpoint *ep)
		ep->next_packet_read_pos %= MAX_URBS;

		/* take URB out of FIFO */
		if (!list_empty(&ep->ready_playback_urbs))
		if (!list_empty(&ep->ready_playback_urbs)) {
		ctx = list_first_entry(&ep->ready_playback_urbs,
		struct snd_urb_ctx, ready_list);
		list_del_init(&ctx->ready_list);
		}
		}
		spin_unlock_irqrestore(&ep->lock, flags);

		if (ctx == NULL)
		return;

		list_del_init(&ctx->ready_list);

		/* copy over the length information */
		for (i = 0; i < packet->packets; i++)
		ctx->packet_size[i] = packet->packet_size[i];

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