Commit ab6bc441 authored by Xu Yilun's avatar Xu Yilun Committed by Jason Gunthorpe
Browse files

iommufd: Rename some shortterm-related identifiers 

Rename the shortterm-related identifiers to wait-related.

The usage of shortterm_users refcount is now beyond its name.  It is
also used for references which live longer than an ioctl execution.
E.g. vdev holds idev's shortterm_users refcount on vdev allocation,
releases it during idev's pre_destroy(). Rename the refcount as
wait_cnt, since it is always used to sync the referencing & the
destruction of the object by waiting for it to go to zero.

List all changed identifiers:

  iommufd_object::shortterm_users -> iommufd_object::wait_cnt
  REMOVE_WAIT_SHORTTERM -> REMOVE_WAIT
  iommufd_object_dec_wait_shortterm() -> iommufd_object_dec_wait()
  zerod_shortterm -> zerod_wait_cnt

No functional change intended.

Link: https://patch.msgid.link/r/20250716070349.1807226-9-yilun.xu@linux.intel.com


Suggested-by: default avatarKevin Tian <kevin.tian@intel.com>
Suggested-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Reviewed-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Reviewed-by: default avatarNicolin Chen <nicolinc@nvidia.com>
Tested-by: default avatarNicolin Chen <nicolinc@nvidia.com>
Signed-off-by: default avatarXu Yilun <yilun.xu@linux.intel.com>
Signed-off-by: default avatarJason Gunthorpe <jgg@nvidia.com>
parent 39a369c3

drivers/iommu/iommufd/device.c

+3 −3
Original line number Diff line number Diff line
@@ -152,8 +152,8 @@ static void iommufd_device_remove_vdev(struct iommufd_device *idev) 
	/*

	 * An ongoing vdev destroy ioctl has removed the vdev from the object

	 * xarray, but has not finished iommufd_vdevice_destroy() yet as it

	 * needs the same mutex. We exit the locking then wait on short term

	 * users for the vdev destruction.

	 * needs the same mutex. We exit the locking then wait on wait_cnt

	 * reference for the vdev destruction.

	 */

	if (IS_ERR(vdev))

		goto out_unlock;
@@ -184,7 +184,7 @@ void iommufd_device_pre_destroy(struct iommufd_object *obj) 
	struct iommufd_device *idev =

		container_of(obj, struct iommufd_device, obj);



	/* Release the short term users on this */

	/* Release the wait_cnt reference on this */

	iommufd_device_remove_vdev(idev);

}

drivers/iommu/iommufd/iommufd_private.h

+9 −9
Original line number Diff line number Diff line
@@ -169,7 +169,7 @@ static inline bool iommufd_lock_obj(struct iommufd_object *obj) 
{

	if (!refcount_inc_not_zero(&obj->users))

		return false;

	if (!refcount_inc_not_zero(&obj->shortterm_users)) {

	if (!refcount_inc_not_zero(&obj->wait_cnt)) {

		/*

		 * If the caller doesn't already have a ref on obj this must be

		 * called under the xa_lock. Otherwise the caller is holding a
@@ -187,11 +187,11 @@ static inline void iommufd_put_object(struct iommufd_ctx *ictx, 
				      struct iommufd_object *obj)

{

	/*

	 * Users first, then shortterm so that REMOVE_WAIT_SHORTTERM never sees

	 * a spurious !0 users with a 0 shortterm_users.

	 * Users first, then wait_cnt so that REMOVE_WAIT never sees a spurious

	 * !0 users with a 0 wait_cnt.

	 */

	refcount_dec(&obj->users);

	if (refcount_dec_and_test(&obj->shortterm_users))

	if (refcount_dec_and_test(&obj->wait_cnt))

		wake_up_interruptible_all(&ictx->destroy_wait);

}
@@ -202,7 +202,7 @@ void iommufd_object_finalize(struct iommufd_ctx *ictx, 
			     struct iommufd_object *obj);



enum {

	REMOVE_WAIT_SHORTTERM	= BIT(0),

	REMOVE_WAIT		= BIT(0),

	REMOVE_OBJ_TOMBSTONE	= BIT(1),

};

int iommufd_object_remove(struct iommufd_ctx *ictx,
@@ -211,15 +211,15 @@ int iommufd_object_remove(struct iommufd_ctx *ictx, 


/*

 * The caller holds a users refcount and wants to destroy the object. At this

 * point the caller has no shortterm_users reference and at least the xarray

 * will be holding one.

 * point the caller has no wait_cnt reference and at least the xarray will be

 * holding one.

 */

static inline void iommufd_object_destroy_user(struct iommufd_ctx *ictx,

					       struct iommufd_object *obj)

{

	int ret;



	ret = iommufd_object_remove(ictx, obj, obj->id, REMOVE_WAIT_SHORTTERM);

	ret = iommufd_object_remove(ictx, obj, obj->id, REMOVE_WAIT);



	/*

	 * If there is a bug and we couldn't destroy the object then we did put
@@ -239,7 +239,7 @@ static inline void iommufd_object_tombstone_user(struct iommufd_ctx *ictx, 
	int ret;



	ret = iommufd_object_remove(ictx, obj, obj->id,

				    REMOVE_WAIT_SHORTTERM | REMOVE_OBJ_TOMBSTONE);

				    REMOVE_WAIT | REMOVE_OBJ_TOMBSTONE);



	/*

	 * If there is a bug and we couldn't destroy the object then we did put

drivers/iommu/iommufd/main.c

+20 −19
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ struct iommufd_object *_iommufd_object_alloc(struct iommufd_ctx *ictx, 
		return ERR_PTR(-ENOMEM);

	obj->type = type;

	/* Starts out bias'd by 1 until it is removed from the xarray */

	refcount_set(&obj->shortterm_users, 1);

	refcount_set(&obj->wait_cnt, 1);

	refcount_set(&obj->users, 1);



	/*
@@ -155,22 +155,22 @@ struct iommufd_object *iommufd_get_object(struct iommufd_ctx *ictx, u32 id, 
	return obj;

}



static int iommufd_object_dec_wait_shortterm(struct iommufd_ctx *ictx,

static int iommufd_object_dec_wait(struct iommufd_ctx *ictx,

				   struct iommufd_object *to_destroy)

{

	if (refcount_dec_and_test(&to_destroy->shortterm_users))

	if (refcount_dec_and_test(&to_destroy->wait_cnt))

		return 0;



	if (iommufd_object_ops[to_destroy->type].pre_destroy)

		iommufd_object_ops[to_destroy->type].pre_destroy(to_destroy);



	if (wait_event_timeout(ictx->destroy_wait,

			       refcount_read(&to_destroy->shortterm_users) == 0,

			       refcount_read(&to_destroy->wait_cnt) == 0,

			       msecs_to_jiffies(60000)))

		return 0;



	pr_crit("Time out waiting for iommufd object to become free\n");

	refcount_inc(&to_destroy->shortterm_users);

	refcount_inc(&to_destroy->wait_cnt);

	return -EBUSY;

}
@@ -184,17 +184,18 @@ int iommufd_object_remove(struct iommufd_ctx *ictx, 
{

	struct iommufd_object *obj;

	XA_STATE(xas, &ictx->objects, id);

	bool zerod_shortterm = false;

	bool zerod_wait_cnt = false;

	int ret;



	/*

	 * The purpose of the shortterm_users is to ensure deterministic

	 * destruction of objects used by external drivers and destroyed by this

	 * function. Any temporary increment of the refcount must increment

	 * shortterm_users, such as during ioctl execution.

	 * The purpose of the wait_cnt is to ensure deterministic destruction

	 * of objects used by external drivers and destroyed by this function.

	 * Incrementing this wait_cnt should either be short lived, such as

	 * during ioctl execution, or be revoked and blocked during

	 * pre_destroy(), such as vdev holding the idev's refcount.

	 */

	if (flags & REMOVE_WAIT_SHORTTERM) {

		ret = iommufd_object_dec_wait_shortterm(ictx, to_destroy);

	if (flags & REMOVE_WAIT) {

		ret = iommufd_object_dec_wait(ictx, to_destroy);

		if (ret) {

			/*

			 * We have a bug. Put back the callers reference and
@@ -203,7 +204,7 @@ int iommufd_object_remove(struct iommufd_ctx *ictx, 
			refcount_dec(&to_destroy->users);

			return ret;

		}

		zerod_shortterm = true;

		zerod_wait_cnt = true;

	}



	xa_lock(&ictx->objects);
@@ -235,11 +236,11 @@ int iommufd_object_remove(struct iommufd_ctx *ictx, 
	xa_unlock(&ictx->objects);



	/*

	 * Since users is zero any positive users_shortterm must be racing

	 * Since users is zero any positive wait_cnt must be racing

	 * iommufd_put_object(), or we have a bug.

	 */

	if (!zerod_shortterm) {

		ret = iommufd_object_dec_wait_shortterm(ictx, obj);

	if (!zerod_wait_cnt) {

		ret = iommufd_object_dec_wait(ictx, obj);

		if (WARN_ON(ret))

			return ret;

	}
@@ -249,9 +250,9 @@ int iommufd_object_remove(struct iommufd_ctx *ictx, 
	return 0;



err_xa:

	if (zerod_shortterm) {

	if (zerod_wait_cnt) {

		/* Restore the xarray owned reference */

		refcount_set(&obj->shortterm_users, 1);

		refcount_set(&obj->wait_cnt, 1);

	}

	xa_unlock(&ictx->objects);

drivers/iommu/iommufd/viommu.c

+2 −2
Original line number Diff line number Diff line
@@ -205,8 +205,8 @@ int iommufd_vdevice_alloc_ioctl(struct iommufd_ucmd *ucmd) 
	vdev->viommu = viommu;

	refcount_inc(&viommu->obj.users);

	/*

	 * A short term users reference is held on the idev so long as we have

	 * the pointer. iommufd_device_pre_destroy() will revoke it before the

	 * A wait_cnt reference is held on the idev so long as we have the

	 * pointer. iommufd_device_pre_destroy() will revoke it before the

	 * idev real destruction.

	 */

	vdev->idev = idev;

include/linux/iommufd.h

+7 −1
Original line number Diff line number Diff line
@@ -46,7 +46,13 @@ enum iommufd_object_type { 


/* Base struct for all objects with a userspace ID handle. */

struct iommufd_object {

	refcount_t shortterm_users;

	/*

	 * Destroy will sleep and wait for wait_cnt to go to zero. This allows

	 * concurrent users of the ID to reliably avoid causing a spurious

	 * destroy failure. Incrementing this count should either be short

	 * lived or be revoked and blocked during pre_destroy().

	 */

	refcount_t wait_cnt;

	refcount_t users;

	enum iommufd_object_type type;

	unsigned int id;