linux-kernel - [PATCH 4.0 16/60] vfio: Fix runaway interruptible timeout

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Date:	Fri, 15 May 2015 16:14:17 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Alex Williamson <alex.williamson@...hat.com>
Subject: [PATCH 4.0 16/60] vfio: Fix runaway interruptible timeout

4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alex Williamson <alex.williamson@...hat.com>

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.

Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
Fixes: 13060b64b819
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -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);
 


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