From b70f5fa043b318659c936d8c3c696250e6528944 Mon Sep 17 00:00:00 2001
From: Daniel Stodden <daniel.stodden@citrix.com>
Date: Fri, 30 Apr 2010 22:01:19 +0000
Subject: blkfront: Lock blkfront_info when closing
The bdev .open/.release fops race against backend switches to Closing,
handled by the XenBus thread.
The original code attempted to serialize block device holders and
xenbus only via bd_mutex. This is insufficient, the info->bd pointer
may already be stale (or null) while xenbus tries to bump up the
refcount.
Protect blkfront_info with a dedicated mutex.
Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
drivers/block/xen-blkfront.c | 61 +++++++++++++++++++++++++++++---------------
1 file changed, 40 insertions(+), 21 deletions(-)
(limited to 'drivers/block')
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index d4cb7fd82b4c..1e406f0331e7 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -79,6 +79,7 @@ static const struct block_device_operations xlvbd_block_fops;
*/
struct blkfront_info
{
+ struct mutex mutex;
struct xenbus_device *xbdev;
struct gendisk *gd;
int vdevice;
@@ -804,7 +805,6 @@ again:
return err;
}
-
/**
* Entry point to this code when a new device is created. Allocate the basic
* structures and the ring buffer for communication with the backend, and
@@ -836,6 +836,7 @@ static int blkfront_probe(struct xenbus_device *dev,
return -ENOMEM;
}
+ mutex_init(&info->mutex);
info->xbdev = dev;
info->vdevice = vdevice;
info->connected = BLKIF_STATE_DISCONNECTED;
@@ -951,6 +952,43 @@ static int blkfront_resume(struct xenbus_device *dev)
return err;
}
+static void
+blkfront_closing(struct blkfront_info *info)
+{
+ struct xenbus_device *xbdev = info->xbdev;
+ struct block_device *bdev = NULL;
+
+ mutex_lock(&info->mutex);
+
+ if (xbdev->state == XenbusStateClosing) {
+ mutex_unlock(&info->mutex);
+ return;
+ }
+
+ if (info->gd)
+ bdev = bdget_disk(info->gd, 0);
+
+ mutex_unlock(&info->mutex);
+
+ if (!bdev) {
+ xenbus_frontend_closed(xbdev);
+ return;
+ }
+
+ mutex_lock(&bdev->bd_mutex);
+
+ if (info->users) {
+ xenbus_dev_error(xbdev, -EBUSY,
+ "Device in use; refusing to close");
+ xenbus_switch_state(xbdev, XenbusStateClosing);
+ } else {
+ xlvbd_release_gendisk(info);
+ xenbus_frontend_closed(xbdev);
+ }
+
+ mutex_unlock(&bdev->bd_mutex);
+ bdput(bdev);
+}
/*
* Invoked when the backend is finally 'ready' (and has told produced
@@ -1034,7 +1072,6 @@ static void blkback_changed(struct xenbus_device *dev,
enum xenbus_state backend_state)
{
struct blkfront_info *info = dev_get_drvdata(&dev->dev);
- struct block_device *bd;
dev_dbg(&dev->dev, "blkfront:blkback_changed to state %d.\n", backend_state);
@@ -1051,25 +1088,7 @@ static void blkback_changed(struct xenbus_device *dev,
break;
case XenbusStateClosing:
- if (info->gd == NULL) {
- xenbus_frontend_closed(dev);
- break;
- }
- bd = bdget_disk(info->gd, 0);
- if (bd == NULL)
- xenbus_dev_fatal(dev, -ENODEV, "bdget failed");
-
- mutex_lock(&bd->bd_mutex);
- if (info->users > 0)
- xenbus_dev_error(dev, -EBUSY,
- "Device in use; refusing to close");
- else {
- xlvbd_release_gendisk(info);
- xenbus_frontend_closed(info->xbdev);
- }
-
- mutex_unlock(&bd->bd_mutex);
- bdput(bd);
+ blkfront_closing(info);
break;
}
}
--
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