From b70f5fa043b318659c936d8c3c696250e6528944 Mon Sep 17 00:00:00 2001 From: Daniel Stodden Date: Fri, 30 Apr 2010 22:01:19 +0000 Subject: [PATCH] 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 Signed-off-by: Jeremy Fitzhardinge --- drivers/block/xen-blkfront.c | 61 +++++++++++++++++++++++------------- 1 file changed, 40 insertions(+), 21 deletions(-) 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; } } -- 2.20.1