[PATCH 2/6] media: msi2500: Return queued buffers on start_streaming() failure

[Valery Borovsky]

The vb2 framework hands buffers to the driver via buf_queue() before
calling start_streaming().  If start_streaming() returns an error
without first returning those buffers via vb2_buffer_done(),
vb2_start_streaming() fires WARN_ON(owned_by_drv_count) and the queued
buffers leak.

msi2500_start_streaming() had five error paths that all hit this trap
and were further tangled by ret-overwriting between calls:

  - -ENODEV when the USB device was already disconnected
  - -ERESTARTSYS when mutex_lock_interruptible() was interrupted
  - msi2500_set_usb_adc() failure: ret was silently overwritten by
    the next call (msi2500_isoc_init), so the error was lost entirely
  - msi2500_isoc_init() failure: cleanup_queued_bufs was called, but
    the function then fell through to msi2500_ctrl_msg() and again
    masked the original error by overwriting ret
  - msi2500_ctrl_msg(CMD_START_STREAMING) failure: no cleanup at all,
    leaving isoc URBs submitted with no way for the driver to consume
    them

Consolidate the error paths into a small goto chain.  Every failure
now stops the function, drains the queued-buffer list, and returns
the real error code.  The ctrl_msg failure path also rolls back the
preceding msi2500_isoc_init() via msi2500_isoc_cleanup() before
unlocking and draining.

The cleanup helper takes a vb2_buffer_state argument so that the
start_streaming error paths can pass VB2_BUF_STATE_QUEUED (as
expected by userspace on start_streaming failure) while stop_streaming
keeps its existing VB2_BUF_STATE_ERROR semantics.

This mirrors the uvcvideo fix in commit 4cf3b6fd54eb ("media: uvcvideo:
Return queued buffers on start_streaming() failure").

Fixes: 977e444f59ad ("[media] Mirics MSi3101 SDR Dongle driver")
Cc: stable at vger.kernel.org
Signed-off-by: Valery Borovsky <vebohr at gmail.com>
---
 drivers/media/usb/msi2500/msi2500.c | 32 +++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/media/usb/msi2500/msi2500.c b/drivers/media/usb/msi2500/msi2500.c
index 1ff98956b680..0614087c3c3c 100644
--- a/drivers/media/usb/msi2500/msi2500.c
+++ b/drivers/media/usb/msi2500/msi2500.c
@@ -541,7 +541,8 @@ static int msi2500_isoc_init(struct msi2500_dev *dev)
 }
 
 /* Must be called with vb_queue_lock hold */
-static void msi2500_cleanup_queued_bufs(struct msi2500_dev *dev)
+static void msi2500_cleanup_queued_bufs(struct msi2500_dev *dev,
+					enum vb2_buffer_state state)
 {
 	unsigned long flags;
 
@@ -554,7 +555,7 @@ static void msi2500_cleanup_queued_bufs(struct msi2500_dev *dev)
 		buf = list_entry(dev->queued_bufs.next,
 				 struct msi2500_frame_buf, list);
 		list_del(&buf->list);
-		vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_ERROR);
+		vb2_buffer_done(&buf->vb.vb2_buf, state);
 	}
 	spin_unlock_irqrestore(&dev->queued_bufs_lock, flags);
 }
@@ -830,25 +831,40 @@ static int msi2500_start_streaming(struct vb2_queue *vq, unsigned int count)
 
 	dev_dbg(dev->dev, "\n");
 
-	if (!dev->udev)
-		return -ENODEV;
+	if (!dev->udev) {
+		ret = -ENODEV;
+		goto err_cleanup;
+	}
 
-	if (mutex_lock_interruptible(&dev->v4l2_lock))
-		return -ERESTARTSYS;
+	if (mutex_lock_interruptible(&dev->v4l2_lock)) {
+		ret = -ERESTARTSYS;
+		goto err_cleanup;
+	}
 
 	/* wake-up tuner */
 	v4l2_subdev_call(dev->v4l2_subdev, core, s_power, 1);
 
 	ret = msi2500_set_usb_adc(dev);
+	if (ret)
+		goto err_unlock_cleanup;
 
 	ret = msi2500_isoc_init(dev);
 	if (ret)
-		msi2500_cleanup_queued_bufs(dev);
+		goto err_unlock_cleanup;
 
 	ret = msi2500_ctrl_msg(dev, CMD_START_STREAMING, 0);
+	if (ret)
+		goto err_isoc_cleanup;
 
 	mutex_unlock(&dev->v4l2_lock);
+	return 0;
 
+err_isoc_cleanup:
+	msi2500_isoc_cleanup(dev);
+err_unlock_cleanup:
+	mutex_unlock(&dev->v4l2_lock);
+err_cleanup:
+	msi2500_cleanup_queued_bufs(dev, VB2_BUF_STATE_QUEUED);
 	return ret;
 }
 
@@ -863,7 +879,7 @@ static void msi2500_stop_streaming(struct vb2_queue *vq)
 	if (dev->udev)
 		msi2500_isoc_cleanup(dev);
 
-	msi2500_cleanup_queued_bufs(dev);
+	msi2500_cleanup_queued_bufs(dev, VB2_BUF_STATE_ERROR);
 
 	/* according to tests, at least 700us delay is required  */
 	msleep(20);
-- 
2.51.0