From: Jason Gunthorpe <jgg@nvidia.com>
Date: Mon, 16 May 2022 20:41:18 -0300
Subject: vfio: Change struct vfio_group::opened from an atomic to bool
Git-commit: c6f4860ef938606117961fac11d8d67497ab299b
Patch-mainline: v5.19-rc1
References: bsc#1205701
This is not a performance path, just use the group_rwsem to protect the
value.
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/r/2-v2-d035a1842d81+1bf-vfio_group_locking_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
drivers/vfio/vfio.c | 46 +++++++++++++++++++++++++++-------------------
1 file changed, 27 insertions(+), 19 deletions(-)
diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 4261eeec9e73..12d4b3efd463 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -73,7 +73,7 @@ struct vfio_group {
struct mutex device_lock;
struct list_head vfio_next;
struct list_head container_next;
- atomic_t opened;
+ bool opened;
enum vfio_group_type type;
unsigned int dev_counter;
struct rw_semaphore group_rwsem;
@@ -1213,30 +1213,30 @@ static int vfio_group_fops_open(struct inode *inode, struct file *filep)
{
struct vfio_group *group =
container_of(inode->i_cdev, struct vfio_group, cdev);
- int opened;
+ int ret;
- /* users can be zero if this races with vfio_group_put() */
- if (!refcount_inc_not_zero(&group->users))
- return -ENODEV;
+ down_write(&group->group_rwsem);
- if (group->type == VFIO_NO_IOMMU && !capable(CAP_SYS_RAWIO)) {
- vfio_group_put(group);
- return -EPERM;
+ /* users can be zero if this races with vfio_group_put() */
+ if (!refcount_inc_not_zero(&group->users)) {
+ ret = -ENODEV;
+ goto err_unlock;
}
- /* Do we need multiple instances of the group open? Seems not. */
- opened = atomic_cmpxchg(&group->opened, 0, 1);
- if (opened) {
- vfio_group_put(group);
- return -EBUSY;
+ if (group->type == VFIO_NO_IOMMU && !capable(CAP_SYS_RAWIO)) {
+ ret = -EPERM;
+ goto err_put;
}
- /* Is something still in use from a previous open? */
- if (group->container) {
- atomic_dec(&group->opened);
- vfio_group_put(group);
- return -EBUSY;
+ /*
+ * Do we need multiple instances of the group open? Seems not.
+ * Is something still in use from a previous open?
+ */
+ if (group->opened || group->container) {
+ ret = -EBUSY;
+ goto err_put;
}
+ group->opened = true;
/* Warn if previous user didn't cleanup and re-init to drop them */
if (WARN_ON(group->notifier.head))
@@ -1244,7 +1244,13 @@ static int vfio_group_fops_open(struct inode *inode, struct file *filep)
filep->private_data = group;
+ up_write(&group->group_rwsem);
return 0;
+err_put:
+ vfio_group_put(group);
+err_unlock:
+ up_write(&group->group_rwsem);
+ return ret;
}
static int vfio_group_fops_release(struct inode *inode, struct file *filep)
@@ -1255,7 +1261,9 @@ static int vfio_group_fops_release(struct inode *inode, struct file *filep)
vfio_group_try_dissolve_container(group);
- atomic_dec(&group->opened);
+ down_write(&group->group_rwsem);
+ group->opened = false;
+ up_write(&group->group_rwsem);
vfio_group_put(group);