Patch "vfio: Fix runaway interruptible timeout" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

vfio: Fix runaway interruptible timeout

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
vfio-fix-runaway-interruptible-timeout.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alex Williamson <[email protected]>
Date: Fri, 1 May 2015 16:31:41 -0600
Subject: vfio: Fix runaway interruptible timeout

From: Alex Williamson <[email protected]>

commit db7d4d7f40215843000cb9d441c9149fd42ea36b upstream.

Commit 13060b64b819 ("vfio: Add and use device request op for vfio bus drivers") incorrectly makes use of an interruptible timeout. When interrupted, the signal remains pending resulting in subsequent timeouts occurring instantly. This makes the loop spin at a much higher rate than intended.

Instead of making this completely non-interruptible, we can change this into a sort of interruptible-once behavior and use the "once" to log debug information. The driver API doesn't allow us to abort and return an error code.

---
 drivers/vfio/vfio.c |   21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

@@ -711,6 +711,8 @@ void *vfio_del_group_dev(struct device *
 	void *device_data = device->device_data;
 	struct vfio_unbound_dev *unbound;
 	unsigned int i = 0;
+	long ret;
+	bool interrupted = false;
 
 	/*
 	 * The group exists so long as we have a device reference.  Get

@@ -756,9 +758,22 @@ void *vfio_del_group_dev(struct device *
 
 		vfio_device_put(device);
 
-	} while (wait_event_interruptible_timeout(vfio.release_q,
-						  !vfio_dev_present(group, dev),
-						  HZ * 10) <= 0);
+		if (interrupted) {
+			ret = wait_event_timeout(vfio.release_q,
+					!vfio_dev_present(group, dev), HZ * 10);
+		} else {
+			ret = wait_event_interruptible_timeout(vfio.release_q,
+					!vfio_dev_present(group, dev), HZ * 10);
+			if (ret == -ERESTARTSYS) {
+				interrupted = true;
+				dev_warn(dev,
+					 "Device is currently in use, task"
+					 " \"%s\" (%d) "
+					 "blocked until device is released",
+					 current->comm, task_pid_nr(current));
+			}
+		}
+	} while (ret <= 0);
 
 	vfio_group_put(group);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/vfio-fix-runaway-interruptible-timeout.patch