staging: line6: alloc/free buffers in hw_params/hw_free

It is unsafe to free buffers in line6_pcm_stop(), which is not allowed
to sleep, since urbs cannot be killed completely there and only
unlinked.  This means I/O may still be in progress and the URB
completion function still gets invoked.  This may result in memory
corruption when buffer_in is freed but I/O is still pending.

Additionally, line6_pcm_start() is not supposed to sleep so it should
not use kmalloc(GFP_KERNEL).

These issues can be resolved by performing buffer allocation/freeing in
the .hw_params/.hw_free callbacks instead.  The ALSA documentation also
recommends doing buffer allocation/freeing in these callbacks.
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/line6/capture.c

@@ -9,6 +9,7 @@
  *
  */
 
+#include <linux/slab.h>
 #include <sound/core.h>
 #include <sound/pcm.h>
 #include <sound/pcm_params.h>
@@ -319,6 +320,15 @@ static int snd_line6_capture_hw_params(struct snd_pcm_substream *substream,
 	}
 	/* -- [FD] end */
 
+	line6pcm->buffer_in = kmalloc(LINE6_ISO_BUFFERS * LINE6_ISO_PACKETS *
+				      line6pcm->max_packet_size, GFP_KERNEL);
+
+	if (!line6pcm->buffer_in) {
+		dev_err(line6pcm->line6->ifcdev,
+			"cannot malloc capture buffer\n");
+		return -ENOMEM;
+	}
+
 	ret = snd_pcm_lib_malloc_pages(substream,
 				       params_buffer_bytes(hw_params));
 	if (ret < 0)
@@ -331,6 +341,11 @@ static int snd_line6_capture_hw_params(struct snd_pcm_substream *substream,
 /* hw_free capture callback */
 static int snd_line6_capture_hw_free(struct snd_pcm_substream *substream)
 {
+	struct snd_line6_pcm *line6pcm = snd_pcm_substream_chip(substream);
+
+	line6_unlink_wait_clear_audio_in_urbs(line6pcm);
+	kfree(line6pcm->buffer_in);
+	line6pcm->buffer_in = NULL;
 	return snd_pcm_lib_free_pages(substream);
 }
 

drivers/staging/line6/pcm.c

@@ -119,16 +119,6 @@ int line6_pcm_start(struct snd_line6_pcm *line6pcm, int channels)
 		if (line6pcm->active_urb_in | line6pcm->unlink_urb_in)
 			return -EBUSY;
 
-		line6pcm->buffer_in =
-		    kmalloc(LINE6_ISO_BUFFERS * LINE6_ISO_PACKETS *
-			    line6pcm->max_packet_size, GFP_KERNEL);
-
-		if (!line6pcm->buffer_in) {
-			dev_err(line6pcm->line6->ifcdev,
-				"cannot malloc capture buffer\n");
-			return -ENOMEM;
-		}
-
 		line6pcm->count_in = 0;
 		line6pcm->prev_fsize = 0;
 		err = line6_submit_audio_in_all_urbs(line6pcm);
@@ -147,16 +137,6 @@ int line6_pcm_start(struct snd_line6_pcm *line6pcm, int channels)
 		if (line6pcm->active_urb_out | line6pcm->unlink_urb_out)
 			return -EBUSY;
 
-		line6pcm->buffer_out =
-		    kmalloc(LINE6_ISO_BUFFERS * LINE6_ISO_PACKETS *
-			    line6pcm->max_packet_size, GFP_KERNEL);
-
-		if (!line6pcm->buffer_out) {
-			dev_err(line6pcm->line6->ifcdev,
-				"cannot malloc playback buffer\n");
-			return -ENOMEM;
-		}
-
 		line6pcm->count_out = 0;
 		err = line6_submit_audio_out_all_urbs(line6pcm);
 
@@ -178,15 +158,11 @@ int line6_pcm_stop(struct snd_line6_pcm *line6pcm, int channels)
 	if (((flags_old & MASK_CAPTURE) != 0) &&
 	    ((flags_new & MASK_CAPTURE) == 0)) {
 		line6_unlink_audio_in_urbs(line6pcm);
-		kfree(line6pcm->buffer_in);
-		line6pcm->buffer_in = NULL;
 	}
 
 	if (((flags_old & MASK_PLAYBACK) != 0) &&
 	    ((flags_new & MASK_PLAYBACK) == 0)) {
 		line6_unlink_audio_out_urbs(line6pcm);
-		kfree(line6pcm->buffer_out);
-		line6pcm->buffer_out = NULL;
 	}
 #if LINE6_BACKUP_MONITOR_SIGNAL
 	kfree(line6pcm->prev_fbuf);

drivers/staging/line6/playback.c

@@ -9,6 +9,7 @@
  *
  */
 
+#include <linux/slab.h>
 #include <sound/core.h>
 #include <sound/pcm.h>
 #include <sound/pcm_params.h>
@@ -469,6 +470,15 @@ static int snd_line6_playback_hw_params(struct snd_pcm_substream *substream,
 	}
 	/* -- [FD] end */
 
+	line6pcm->buffer_out = kmalloc(LINE6_ISO_BUFFERS * LINE6_ISO_PACKETS *
+				       line6pcm->max_packet_size, GFP_KERNEL);
+
+	if (!line6pcm->buffer_out) {
+		dev_err(line6pcm->line6->ifcdev,
+			"cannot malloc playback buffer\n");
+		return -ENOMEM;
+	}
+
 	ret = snd_pcm_lib_malloc_pages(substream,
 				       params_buffer_bytes(hw_params));
 	if (ret < 0)
@@ -481,6 +491,11 @@ static int snd_line6_playback_hw_params(struct snd_pcm_substream *substream,
 /* hw_free playback callback */
 static int snd_line6_playback_hw_free(struct snd_pcm_substream *substream)
 {
+	struct snd_line6_pcm *line6pcm = snd_pcm_substream_chip(substream);
+
+	line6_unlink_wait_clear_audio_out_urbs(line6pcm);
+	kfree(line6pcm->buffer_out);
+	line6pcm->buffer_out = NULL;
 	return snd_pcm_lib_free_pages(substream);
 }