On 3/17/21 12:21 AM, Tetsuo Handa wrote:

Shuah, this driver is getting more and more cryptic and buggy.
Please explain the strategy for serialization before you write patches.

quoted

- Fix attach_store() to check usbip_event_happened() before
   waking up threads.

No, this helps nothing.

quoted

diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
index c4b4256e5dad3..f0a770adebd97 100644
--- a/drivers/usb/usbip/vhci_sysfs.c
+++ b/drivers/usb/usbip/vhci_sysfs.c

@@ -418,6 +418,15 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
  	spin_unlock_irqrestore(&vhci->lock, flags);
  	/* end the lock */
  
+	if (usbip_event_happened(&vdev->ud)) {
+		/*
+		 * something went wrong - event handler shutting
+		 * the connection and doing reset - bail out
+		 */
+		dev_err(dev, "Event happended - handler is active\n");
+		return -EAGAIN;
+	}
+

detach_store() can queue shutdown event as soon as reaching "/* end the lock */" line
but attach_store() might be preempted immediately after verifying that
usbip_event_happened() was false (i.e. at this location) in order to wait for
shutdown event posted by detach_store() to be processed.

Yes. I haven't sent the patch for that reason. I am trying to test a
solution. I haven't come up with a solution yet.

Holding event_lock isn't the right solution. I am not going to accept
that. This is a window that gets triggered by syzbot injecting errors
in a sequence. Fixing this should be done taking other moving parts of
the driver into account.

thanks,
-- Shuah