From: Jason Gunthorpe <jgg@nvidia.com>
To: Alex Williamson <alex.williamson@redhat.com>,
Cornelia Huck <cohuck@redhat.com>,
kvm@vger.kernel.org
Subject: [PATCH 1/2] vfio: Remove the vfio_group->users and users_comp
Date: Thu, 29 Sep 2022 11:59:24 -0300 [thread overview]
Message-ID: <1-v1-917e3647f123+b1a-vfio_group_users_jgg@nvidia.com> (raw)
In-Reply-To: <0-v1-917e3647f123+b1a-vfio_group_users_jgg@nvidia.com>
Kevin points out that the users is really just tracking if
group->opened_file is set, so we can simplify this code to a wait_queue
that looks for !opened_file under the group_rwsem.
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/vfio/vfio.h | 3 +--
drivers/vfio/vfio_main.c | 45 +++++++++++++++++-----------------------
2 files changed, 20 insertions(+), 28 deletions(-)
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
index 039e3208d286fa..78b362a9250113 100644
--- a/drivers/vfio/vfio.h
+++ b/drivers/vfio/vfio.h
@@ -48,8 +48,6 @@ struct vfio_group {
* reaches 0 then the iommu_group is invalid.
*/
refcount_t drivers;
- refcount_t users;
- struct completion users_comp;
unsigned int container_users;
struct iommu_group *iommu_group;
struct vfio_container *container;
@@ -61,6 +59,7 @@ struct vfio_group {
struct rw_semaphore group_rwsem;
struct kvm *kvm;
struct file *opened_file;
+ struct swait_queue_head opened_file_wait;
struct blocking_notifier_head notifier;
};
diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index f19171cad9a25f..57a7576a96a61b 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -186,10 +186,9 @@ static struct vfio_group *vfio_group_alloc(struct iommu_group *iommu_group,
cdev_init(&group->cdev, &vfio_group_fops);
group->cdev.owner = THIS_MODULE;
- refcount_set(&group->users, 1);
refcount_set(&group->drivers, 1);
- init_completion(&group->users_comp);
init_rwsem(&group->group_rwsem);
+ init_swait_queue_head(&group->opened_file_wait);
INIT_LIST_HEAD(&group->device_list);
mutex_init(&group->device_lock);
group->iommu_group = iommu_group;
@@ -245,12 +244,6 @@ static struct vfio_group *vfio_create_group(struct iommu_group *iommu_group,
return ret;
}
-static void vfio_group_put(struct vfio_group *group)
-{
- if (refcount_dec_and_test(&group->users))
- complete(&group->users_comp);
-}
-
static void vfio_device_remove_group(struct vfio_device *device)
{
struct vfio_group *group = device->group;
@@ -270,10 +263,6 @@ static void vfio_device_remove_group(struct vfio_device *device)
* cdev_device_add() will fail due to the name aready existing.
*/
cdev_device_del(&group->cdev, &group->dev);
- mutex_unlock(&vfio.group_lock);
-
- /* Matches the get from vfio_group_alloc() */
- vfio_group_put(group);
/*
* Before we allow the last driver in the group to be unplugged the
@@ -281,7 +270,13 @@ static void vfio_device_remove_group(struct vfio_device *device)
* is because the group->iommu_group pointer should only be used so long
* as a device driver is attached to a device in the group.
*/
- wait_for_completion(&group->users_comp);
+ while (group->opened_file) {
+ mutex_unlock(&vfio.group_lock);
+ swait_event_idle_exclusive(group->opened_file_wait,
+ !group->opened_file);
+ mutex_lock(&vfio.group_lock);
+ }
+ mutex_unlock(&vfio.group_lock);
/*
* These data structures all have paired operations that can only be
@@ -906,15 +901,18 @@ static int vfio_group_fops_open(struct inode *inode, struct file *filep)
down_write(&group->group_rwsem);
- /* users can be zero if this races with vfio_device_remove_group() */
- if (!refcount_inc_not_zero(&group->users)) {
+ /*
+ * drivers can be zero if this races with vfio_device_remove_group(), it
+ * will be stable at 0 under the group rwsem
+ */
+ if (refcount_read(&group->drivers) == 0) {
ret = -ENODEV;
- goto err_unlock;
+ goto out_unlock;
}
if (group->type == VFIO_NO_IOMMU && !capable(CAP_SYS_RAWIO)) {
ret = -EPERM;
- goto err_put;
+ goto out_unlock;
}
/*
@@ -922,16 +920,12 @@ static int vfio_group_fops_open(struct inode *inode, struct file *filep)
*/
if (group->opened_file) {
ret = -EBUSY;
- goto err_put;
+ goto out_unlock;
}
group->opened_file = filep;
filep->private_data = group;
-
- up_write(&group->group_rwsem);
- return 0;
-err_put:
- vfio_group_put(group);
-err_unlock:
+ ret = 0;
+out_unlock:
up_write(&group->group_rwsem);
return ret;
}
@@ -952,8 +946,7 @@ static int vfio_group_fops_release(struct inode *inode, struct file *filep)
vfio_group_detach_container(group);
group->opened_file = NULL;
up_write(&group->group_rwsem);
-
- vfio_group_put(group);
+ swake_up_one(&group->opened_file_wait);
return 0;
}
--
2.37.3
next prev parent reply other threads:[~2022-09-29 14:59 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-29 14:59 [PATCH 0/2] Simplify some of the locking in vfio_group Jason Gunthorpe
2022-09-29 14:59 ` Jason Gunthorpe [this message]
2022-09-30 8:58 ` [PATCH 1/2] vfio: Remove the vfio_group->users and users_comp Tian, Kevin
2022-09-29 14:59 ` [PATCH 2/2] vfio: Change vfio_group->group_rwsem to a mutex Jason Gunthorpe
2022-09-30 9:05 ` Tian, Kevin
2022-09-30 21:31 ` [PATCH 0/2] Simplify some of the locking in vfio_group Alex Williamson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1-v1-917e3647f123+b1a-vfio_group_users_jgg@nvidia.com \
--to=jgg@nvidia.com \
--cc=alex.williamson@redhat.com \
--cc=cohuck@redhat.com \
--cc=kvm@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.