IB/uverbs: Don't serialize with ib_uverbs_idr_mutex

Currently, all userspace verbs operations that call into the kernel
are serialized by ib_uverbs_idr_mutex. This can be a scalability
issue for some workloads, especially for devices driven by the ipath
driver, which needs to call into the kernel even for datapath
operations.

Fix this by adding reference counts to the userspace objects, and then
converting ib_uverbs_idr_mutex into a spinlock that only protects the
idrs long enough to take a reference on the object being looked up.
Because remove operations may fail, we have to do a slightly funky
two-step deletion, which is described in the comments at the top of
uverbs_cmd.c.

This also still leaves ib_uverbs_idr_lock as a single lock that is
possibly subject to contention. However, the lock hold time will only
be a single idr operation, so multiple threads should still be able to
make progress, even if ib_uverbs_idr_lock is being ping-ponged.

Surprisingly, these changes even shrink the object code:

add/remove: 23/5 grow/shrink: 4/21 up/down: 633/-693 (-60)

Signed-off-by: Roland Dreier <[e-mail]>

drivers/infiniband/core/uverbs.h

···
 	u32			async_events_reported;
 };
 
-extern struct mutex ib_uverbs_idr_mutex;
+extern spinlock_t ib_uverbs_idr_lock;
 extern struct idr ib_uverbs_pd_idr;
 extern struct idr ib_uverbs_mr_idr;
 extern struct idr ib_uverbs_mw_idr;
···
 extern struct idr ib_uverbs_cq_idr;
 extern struct idr ib_uverbs_qp_idr;
 extern struct idr ib_uverbs_srq_idr;
+
+void idr_remove_uobj(struct idr *idp, struct ib_uobject *uobj);
 
 struct file *ib_uverbs_alloc_event_file(struct ib_uverbs_file *uverbs_file,
 					int is_async, int *fd);

drivers/infiniband/core/uverbs_cmd.c

···
 		(udata)->outlen = (olen);				\
 	} while (0)
 
-static int idr_add_uobj(struct idr *idr, void *obj, struct ib_uobject *uobj)
+/*
+ * The ib_uobject locking scheme is as follows:
+ *
+ * - ib_uverbs_idr_lock protects the uverbs idrs themselves, so it
+ *   needs to be held during all idr operations.  When an object is
+ *   looked up, a reference must be taken on the object's kref before
+ *   dropping this lock.
+ *
+ * - Each object also has an rwsem.  This rwsem must be held for
+ *   reading while an operation that uses the object is performed.
+ *   For example, while registering an MR, the associated PD's
+ *   uobject.mutex must be held for reading.  The rwsem must be held
+ *   for writing while initializing or destroying an object.
+ *
+ * - In addition, each object has a "live" flag.  If this flag is not
+ *   set, then lookups of the object will fail even if it is found in
+ *   the idr.  This handles a reader that blocks and does not acquire
+ *   the rwsem until after the object is destroyed.  The destroy
+ *   operation will set the live flag to 0 and then drop the rwsem;
+ *   this will allow the reader to acquire the rwsem, see that the
+ *   live flag is 0, and then drop the rwsem and its reference to
+ *   object.  The underlying storage will not be freed until the last
+ *   reference to the object is dropped.
+ */
+
+static void init_uobj(struct ib_uobject *uobj, u64 user_handle,
+		      struct ib_ucontext *context)
+{
+	uobj->user_handle = user_handle;
+	uobj->context     = context;
+	kref_init(&uobj->ref);
+	init_rwsem(&uobj->mutex);
+	uobj->live        = 0;
+}
+
+static void release_uobj(struct kref *kref)
+{
+	kfree(container_of(kref, struct ib_uobject, ref));
+}
+
+static void put_uobj(struct ib_uobject *uobj)
+{
+	kref_put(&uobj->ref, release_uobj);
+}
+
+static void put_uobj_read(struct ib_uobject *uobj)
+{
+	up_read(&uobj->mutex);
+	put_uobj(uobj);
+}
+
+static void put_uobj_write(struct ib_uobject *uobj)
+{
+	up_write(&uobj->mutex);
+	put_uobj(uobj);
+}
+
+static int idr_add_uobj(struct idr *idr, struct ib_uobject *uobj)
 {
 	int ret;
 
···
 	if (!idr_pre_get(idr, GFP_KERNEL))
 		return -ENOMEM;
 
+	spin_lock(&ib_uverbs_idr_lock);
 	ret = idr_get_new(idr, uobj, &uobj->id);
+	spin_unlock(&ib_uverbs_idr_lock);
 
 	if (ret == -EAGAIN)
 		goto retry;
 
 	return ret;
+}
+
+void idr_remove_uobj(struct idr *idr, struct ib_uobject *uobj)
+{
+	spin_lock(&ib_uverbs_idr_lock);
+	idr_remove(idr, uobj->id);
+	spin_unlock(&ib_uverbs_idr_lock);
+}
+
+static struct ib_uobject *__idr_get_uobj(struct idr *idr, int id,
+					 struct ib_ucontext *context)
+{
+	struct ib_uobject *uobj;
+
+	spin_lock(&ib_uverbs_idr_lock);
+	uobj = idr_find(idr, id);
+	if (uobj)
+		kref_get(&uobj->ref);
+	spin_unlock(&ib_uverbs_idr_lock);
+
+	return uobj;
+}
+
+static struct ib_uobject *idr_read_uobj(struct idr *idr, int id,
+					struct ib_ucontext *context)
+{
+	struct ib_uobject *uobj;
+
+	uobj = __idr_get_uobj(idr, id, context);
+	if (!uobj)
+		return NULL;
+
+	down_read(&uobj->mutex);
+	if (!uobj->live) {
+		put_uobj_read(uobj);
+		return NULL;
+	}
+
+	return uobj;
+}
+
+static struct ib_uobject *idr_write_uobj(struct idr *idr, int id,
+					 struct ib_ucontext *context)
+{
+	struct ib_uobject *uobj;
+
+	uobj = __idr_get_uobj(idr, id, context);
+	if (!uobj)
+		return NULL;
+
+	down_write(&uobj->mutex);
+	if (!uobj->live) {
+		put_uobj_write(uobj);
+		return NULL;
+	}
+
+	return uobj;
+}
+
+static void *idr_read_obj(struct idr *idr, int id, struct ib_ucontext *context)
+{
+	struct ib_uobject *uobj;
+
+	uobj = idr_read_uobj(idr, id, context);
+	return uobj ? uobj->object : NULL;
+}
+
+static struct ib_pd *idr_read_pd(int pd_handle, struct ib_ucontext *context)
+{
+	return idr_read_obj(&ib_uverbs_pd_idr, pd_handle, context);
+}
+
+static void put_pd_read(struct ib_pd *pd)
+{
+	put_uobj_read(pd->uobject);
+}
+
+static struct ib_cq *idr_read_cq(int cq_handle, struct ib_ucontext *context)
+{
+	return idr_read_obj(&ib_uverbs_cq_idr, cq_handle, context);
+}
+
+static void put_cq_read(struct ib_cq *cq)
+{
+	put_uobj_read(cq->uobject);
+}
+
+static struct ib_ah *idr_read_ah(int ah_handle, struct ib_ucontext *context)
+{
+	return idr_read_obj(&ib_uverbs_ah_idr, ah_handle, context);
+}
+
+static void put_ah_read(struct ib_ah *ah)
+{
+	put_uobj_read(ah->uobject);
+}
+
+static struct ib_qp *idr_read_qp(int qp_handle, struct ib_ucontext *context)
+{
+	return idr_read_obj(&ib_uverbs_qp_idr, qp_handle, context);
+}
+
+static void put_qp_read(struct ib_qp *qp)
+{
+	put_uobj_read(qp->uobject);
+}
+
+static struct ib_srq *idr_read_srq(int srq_handle, struct ib_ucontext *context)
+{
+	return idr_read_obj(&ib_uverbs_srq_idr, srq_handle, context);
+}
+
+static void put_srq_read(struct ib_srq *srq)
+{
+	put_uobj_read(srq->uobject);
 }
 
 ssize_t ib_uverbs_get_context(struct ib_uverbs_file *file,
···
 	if (!uobj)
 		return -ENOMEM;
 
-	uobj->context = file->ucontext;
+	init_uobj(uobj, 0, file->ucontext);
+	down_write(&uobj->mutex);
 
 	pd = file->device->ib_dev->alloc_pd(file->device->ib_dev,
 					    file->ucontext, &udata);
···
 	pd->uobject = uobj;
 	atomic_set(&pd->usecnt, 0);
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	ret = idr_add_uobj(&ib_uverbs_pd_idr, pd, uobj);
+	uobj->object = pd;
+	ret = idr_add_uobj(&ib_uverbs_pd_idr, uobj);
 	if (ret)
-		goto err_up;
+		goto err_idr;
 
 	memset(&resp, 0, sizeof resp);
 	resp.pd_handle = uobj->id;
···
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp)) {
 		ret = -EFAULT;
-		goto err_idr;
+		goto err_copy;
 	}
 
 	mutex_lock(&file->mutex);
 	list_add_tail(&uobj->list, &file->ucontext->pd_list);
 	mutex_unlock(&file->mutex);
 
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	uobj->live = 1;
+
+	up_write(&uobj->mutex);
 
 	return in_len;
 
-err_idr:
-	idr_remove(&ib_uverbs_pd_idr, uobj->id);
+err_copy:
+	idr_remove_uobj(&ib_uverbs_pd_idr, uobj);
 
-err_up:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+err_idr:
 	ib_dealloc_pd(pd);
 
 err:
-	kfree(uobj);
+	put_uobj_write(uobj);
 	return ret;
 }
 
···
 			     int in_len, int out_len)
 {
 	struct ib_uverbs_dealloc_pd cmd;
-	struct ib_pd               *pd;
 	struct ib_uobject          *uobj;
-	int                         ret = -EINVAL;
+	int                         ret;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
+	uobj = idr_write_uobj(&ib_uverbs_pd_idr, cmd.pd_handle, file->ucontext);
+	if (!uobj)
+		return -EINVAL;
 
-	pd = idr_find(&ib_uverbs_pd_idr, cmd.pd_handle);
-	if (!pd || pd->uobject->context != file->ucontext)
-		goto out;
+	ret = ib_dealloc_pd(uobj->object);
+	if (!ret)
+		uobj->live = 0;
 
-	uobj = pd->uobject;
+	put_uobj_write(uobj);
 
-	ret = ib_dealloc_pd(pd);
 	if (ret)
-		goto out;
+		return ret;
 
-	idr_remove(&ib_uverbs_pd_idr, cmd.pd_handle);
+	idr_remove_uobj(&ib_uverbs_pd_idr, uobj);
 
 	mutex_lock(&file->mutex);
 	list_del(&uobj->list);
 	mutex_unlock(&file->mutex);
 
-	kfree(uobj);
+	put_uobj(uobj);
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
-
-	return ret ? ret : in_len;
+	return in_len;
 }
 
 ssize_t ib_uverbs_reg_mr(struct ib_uverbs_file *file,
···
 	if (!obj)
 		return -ENOMEM;
 
-	obj->uobject.context = file->ucontext;
+	init_uobj(&obj->uobject, 0, file->ucontext);
+	down_write(&obj->uobject.mutex);
 
 	/*
 	 * We ask for writable memory if any access flags other than
···
 
 	obj->umem.virt_base = cmd.hca_va;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	pd = idr_find(&ib_uverbs_pd_idr, cmd.pd_handle);
-	if (!pd || pd->uobject->context != file->ucontext) {
-		ret = -EINVAL;
-		goto err_up;
-	}
-
-	if (!pd->device->reg_user_mr) {
-		ret = -ENOSYS;
-		goto err_up;
-	}
+	pd = idr_read_pd(cmd.pd_handle, file->ucontext);
+	if (!pd)
+		goto err_release;
 
 	mr = pd->device->reg_user_mr(pd, &obj->umem, cmd.access_flags, &udata);
 	if (IS_ERR(mr)) {
 		ret = PTR_ERR(mr);
-		goto err_up;
+		goto err_put;
 	}
 
 	mr->device  = pd->device;
···
 	atomic_inc(&pd->usecnt);
 	atomic_set(&mr->usecnt, 0);
 
-	memset(&resp, 0, sizeof resp);
-	resp.lkey = mr->lkey;
-	resp.rkey = mr->rkey;
-
-	ret = idr_add_uobj(&ib_uverbs_mr_idr, mr, &obj->uobject);
+	obj->uobject.object = mr;
+	ret = idr_add_uobj(&ib_uverbs_mr_idr, &obj->uobject);
 	if (ret)
 		goto err_unreg;
 
+	memset(&resp, 0, sizeof resp);
+	resp.lkey      = mr->lkey;
+	resp.rkey      = mr->rkey;
 	resp.mr_handle = obj->uobject.id;
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp)) {
 		ret = -EFAULT;
-		goto err_idr;
+		goto err_copy;
 	}
+
+	put_pd_read(pd);
 
 	mutex_lock(&file->mutex);
 	list_add_tail(&obj->uobject.list, &file->ucontext->mr_list);
 	mutex_unlock(&file->mutex);
 
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	obj->uobject.live = 1;
+
+	up_write(&obj->uobject.mutex);
 
 	return in_len;
 
-err_idr:
-	idr_remove(&ib_uverbs_mr_idr, obj->uobject.id);
+err_copy:
+	idr_remove_uobj(&ib_uverbs_mr_idr, &obj->uobject);
 
 err_unreg:
 	ib_dereg_mr(mr);
 
-err_up:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+err_put:
+	put_pd_read(pd);
 
+err_release:
 	ib_umem_release(file->device->ib_dev, &obj->umem);
 
 err_free:
-	kfree(obj);
+	put_uobj_write(&obj->uobject);
 	return ret;
 }
 
···
 {
 	struct ib_uverbs_dereg_mr cmd;
 	struct ib_mr             *mr;
+	struct ib_uobject	 *uobj;
 	struct ib_umem_object    *memobj;
 	int                       ret = -EINVAL;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
+	uobj = idr_write_uobj(&ib_uverbs_mr_idr, cmd.mr_handle, file->ucontext);
+	if (!uobj)
+		return -EINVAL;
 
-	mr = idr_find(&ib_uverbs_mr_idr, cmd.mr_handle);
-	if (!mr || mr->uobject->context != file->ucontext)
-		goto out;
-
-	memobj = container_of(mr->uobject, struct ib_umem_object, uobject);
+	memobj = container_of(uobj, struct ib_umem_object, uobject);
+	mr     = uobj->object;
 
 	ret = ib_dereg_mr(mr);
-	if (ret)
-		goto out;
+	if (!ret)
+		uobj->live = 0;
 
-	idr_remove(&ib_uverbs_mr_idr, cmd.mr_handle);
+	put_uobj_write(uobj);
+
+	if (ret)
+		return ret;
+
+	idr_remove_uobj(&ib_uverbs_mr_idr, uobj);
 
 	mutex_lock(&file->mutex);
-	list_del(&memobj->uobject.list);
+	list_del(&uobj->list);
 	mutex_unlock(&file->mutex);
 
 	ib_umem_release(file->device->ib_dev, &memobj->umem);
-	kfree(memobj);
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	put_uobj(uobj);
 
-	return ret ? ret : in_len;
+	return in_len;
 }
 
 ssize_t ib_uverbs_create_comp_channel(struct ib_uverbs_file *file,
···
 	struct ib_uverbs_create_cq      cmd;
 	struct ib_uverbs_create_cq_resp resp;
 	struct ib_udata                 udata;
-	struct ib_ucq_object           *uobj;
+	struct ib_ucq_object           *obj;
 	struct ib_uverbs_event_file    *ev_file = NULL;
 	struct ib_cq                   *cq;
 	int                             ret;
···
 	if (cmd.comp_vector >= file->device->num_comp_vectors)
 		return -EINVAL;
 
-	uobj = kmalloc(sizeof *uobj, GFP_KERNEL);
-	if (!uobj)
+	obj = kmalloc(sizeof *obj, GFP_KERNEL);
+	if (!obj)
 		return -ENOMEM;
+
+	init_uobj(&obj->uobject, cmd.user_handle, file->ucontext);
+	down_write(&obj->uobject.mutex);
 
 	if (cmd.comp_channel >= 0) {
 		ev_file = ib_uverbs_lookup_comp_file(cmd.comp_channel);
···
 		}
 	}
 
-	uobj->uobject.user_handle   = cmd.user_handle;
-	uobj->uobject.context       = file->ucontext;
-	uobj->uverbs_file	    = file;
-	uobj->comp_events_reported  = 0;
-	uobj->async_events_reported = 0;
-	INIT_LIST_HEAD(&uobj->comp_list);
-	INIT_LIST_HEAD(&uobj->async_list);
+	obj->uverbs_file	   = file;
+	obj->comp_events_reported  = 0;
+	obj->async_events_reported = 0;
+	INIT_LIST_HEAD(&obj->comp_list);
+	INIT_LIST_HEAD(&obj->async_list);
 
 	cq = file->device->ib_dev->create_cq(file->device->ib_dev, cmd.cqe,
 					     file->ucontext, &udata);
 	if (IS_ERR(cq)) {
 		ret = PTR_ERR(cq);
-		goto err;
+		goto err_file;
 	}
 
 	cq->device        = file->device->ib_dev;
-	cq->uobject       = &uobj->uobject;
+	cq->uobject       = &obj->uobject;
 	cq->comp_handler  = ib_uverbs_comp_handler;
 	cq->event_handler = ib_uverbs_cq_event_handler;
 	cq->cq_context    = ev_file;
 	atomic_set(&cq->usecnt, 0);
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	ret = idr_add_uobj(&ib_uverbs_cq_idr, cq, &uobj->uobject);
+	obj->uobject.object = cq;
+	ret = idr_add_uobj(&ib_uverbs_cq_idr, &obj->uobject);
 	if (ret)
-		goto err_up;
+		goto err_free;
 
 	memset(&resp, 0, sizeof resp);
-	resp.cq_handle = uobj->uobject.id;
+	resp.cq_handle = obj->uobject.id;
 	resp.cqe       = cq->cqe;
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp)) {
 		ret = -EFAULT;
-		goto err_idr;
+		goto err_copy;
 	}
 
 	mutex_lock(&file->mutex);
-	list_add_tail(&uobj->uobject.list, &file->ucontext->cq_list);
+	list_add_tail(&obj->uobject.list, &file->ucontext->cq_list);
 	mutex_unlock(&file->mutex);
 
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	obj->uobject.live = 1;
+
+	up_write(&obj->uobject.mutex);
 
 	return in_len;
 
-err_idr:
-	idr_remove(&ib_uverbs_cq_idr, uobj->uobject.id);
+err_copy:
+	idr_remove_uobj(&ib_uverbs_cq_idr, &obj->uobject);
 
-err_up:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+
+err_free:
 	ib_destroy_cq(cq);
 
-err:
+err_file:
 	if (ev_file)
-		ib_uverbs_release_ucq(file, ev_file, uobj);
-	kfree(uobj);
+		ib_uverbs_release_ucq(file, ev_file, obj);
+
+err:
+	put_uobj_write(&obj->uobject);
 	return ret;
 }
 
···
 		   (unsigned long) cmd.response + sizeof resp,
 		   in_len - sizeof cmd, out_len - sizeof resp);
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	cq = idr_find(&ib_uverbs_cq_idr, cmd.cq_handle);
-	if (!cq || cq->uobject->context != file->ucontext || !cq->device->resize_cq)
-		goto out;
+	cq = idr_read_cq(cmd.cq_handle, file->ucontext);
+	if (!cq)
+		return -EINVAL;
 
 	ret = cq->device->resize_cq(cq, cmd.cqe, &udata);
 	if (ret)
···
 		ret = -EFAULT;
 
 out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	put_cq_read(cq);
 
 	return ret ? ret : in_len;
 }
···
 {
 	struct ib_uverbs_poll_cq       cmd;
 	struct ib_uverbs_poll_cq_resp *resp;
+	struct ib_uobject	      *uobj;
 	struct ib_cq                  *cq;
 	struct ib_wc                  *wc;
 	int                            ret = 0;
···
 		goto out_wc;
 	}
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-	cq = idr_find(&ib_uverbs_cq_idr, cmd.cq_handle);
-	if (!cq || cq->uobject->context != file->ucontext) {
+	uobj = idr_read_uobj(&ib_uverbs_cq_idr, cmd.cq_handle, file->ucontext);
+	if (!uobj) {
 		ret = -EINVAL;
 		goto out;
 	}
+	cq = uobj->object;
 
 	resp->count = ib_poll_cq(cq, cmd.ne, wc);
+
+	put_uobj_read(uobj);
 
 	for (i = 0; i < resp->count; i++) {
 		resp->wc[i].wr_id 	   = wc[i].wr_id;
···
 		ret = -EFAULT;
 
 out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
 	kfree(resp);
 
 out_wc:
···
 				int out_len)
 {
 	struct ib_uverbs_req_notify_cq cmd;
+	struct ib_uobject	      *uobj;
 	struct ib_cq                  *cq;
-	int                            ret = -EINVAL;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-	cq = idr_find(&ib_uverbs_cq_idr, cmd.cq_handle);
-	if (cq && cq->uobject->context == file->ucontext) {
-		ib_req_notify_cq(cq, cmd.solicited_only ?
-					IB_CQ_SOLICITED : IB_CQ_NEXT_COMP);
-		ret = in_len;
-	}
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	uobj = idr_read_uobj(&ib_uverbs_cq_idr, cmd.cq_handle, file->ucontext);
+	if (!uobj)
+		return -EINVAL;
+	cq = uobj->object;
 
-	return ret;
+	ib_req_notify_cq(cq, cmd.solicited_only ?
+			 IB_CQ_SOLICITED : IB_CQ_NEXT_COMP);
+
+	put_uobj_read(uobj);
+
+	return in_len;
 }
 
 ssize_t ib_uverbs_destroy_cq(struct ib_uverbs_file *file,
···
 {
 	struct ib_uverbs_destroy_cq      cmd;
 	struct ib_uverbs_destroy_cq_resp resp;
+	struct ib_uobject		*uobj;
 	struct ib_cq               	*cq;
-	struct ib_ucq_object        	*uobj;
+	struct ib_ucq_object        	*obj;
 	struct ib_uverbs_event_file	*ev_file;
-	u64				 user_handle;
 	int                        	 ret = -EINVAL;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	memset(&resp, 0, sizeof resp);
-
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	cq = idr_find(&ib_uverbs_cq_idr, cmd.cq_handle);
-	if (!cq || cq->uobject->context != file->ucontext)
-		goto out;
-
-	user_handle = cq->uobject->user_handle;
-	uobj        = container_of(cq->uobject, struct ib_ucq_object, uobject);
-	ev_file     = cq->cq_context;
+	uobj = idr_write_uobj(&ib_uverbs_cq_idr, cmd.cq_handle, file->ucontext);
+	if (!uobj)
+		return -EINVAL;
+	cq      = uobj->object;
+	ev_file = cq->cq_context;
+	obj     = container_of(cq->uobject, struct ib_ucq_object, uobject);
 
 	ret = ib_destroy_cq(cq);
-	if (ret)
-		goto out;
+	if (!ret)
+		uobj->live = 0;
 
-	idr_remove(&ib_uverbs_cq_idr, cmd.cq_handle);
+	put_uobj_write(uobj);
+
+	if (ret)
+		return ret;
+
+	idr_remove_uobj(&ib_uverbs_cq_idr, uobj);
 
 	mutex_lock(&file->mutex);
-	list_del(&uobj->uobject.list);
+	list_del(&uobj->list);
 	mutex_unlock(&file->mutex);
 
-	ib_uverbs_release_ucq(file, ev_file, uobj);
+	ib_uverbs_release_ucq(file, ev_file, obj);
 
-	resp.comp_events_reported  = uobj->comp_events_reported;
-	resp.async_events_reported = uobj->async_events_reported;
+	memset(&resp, 0, sizeof resp);
+	resp.comp_events_reported  = obj->comp_events_reported;
+	resp.async_events_reported = obj->async_events_reported;
 
-	kfree(uobj);
+	put_uobj(uobj);
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp))
-		ret = -EFAULT;
+		return -EFAULT;
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
-
-	return ret ? ret : in_len;
+	return in_len;
 }
 
 ssize_t ib_uverbs_create_qp(struct ib_uverbs_file *file,
···
 	struct ib_uverbs_create_qp      cmd;
 	struct ib_uverbs_create_qp_resp resp;
 	struct ib_udata                 udata;
-	struct ib_uqp_object           *uobj;
+	struct ib_uqp_object           *obj;
 	struct ib_pd                   *pd;
 	struct ib_cq                   *scq, *rcq;
 	struct ib_srq                  *srq;
···
 		   (unsigned long) cmd.response + sizeof resp,
 		   in_len - sizeof cmd, out_len - sizeof resp);
 
-	uobj = kmalloc(sizeof *uobj, GFP_KERNEL);
-	if (!uobj)
+	obj = kmalloc(sizeof *obj, GFP_KERNEL);
+	if (!obj)
 		return -ENOMEM;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
+	init_uobj(&obj->uevent.uobject, cmd.user_handle, file->ucontext);
+	down_write(&obj->uevent.uobject.mutex);
 
-	pd  = idr_find(&ib_uverbs_pd_idr, cmd.pd_handle);
-	scq = idr_find(&ib_uverbs_cq_idr, cmd.send_cq_handle);
-	rcq = idr_find(&ib_uverbs_cq_idr, cmd.recv_cq_handle);
-	srq = cmd.is_srq ? idr_find(&ib_uverbs_srq_idr, cmd.srq_handle) : NULL;
+	pd  = idr_read_pd(cmd.pd_handle, file->ucontext);
+	scq = idr_read_cq(cmd.send_cq_handle, file->ucontext);
+	rcq = idr_read_cq(cmd.recv_cq_handle, file->ucontext);
+	srq = cmd.is_srq ? idr_read_srq(cmd.srq_handle, file->ucontext) : NULL;
 
-	if (!pd  || pd->uobject->context  != file->ucontext ||
-	    !scq || scq->uobject->context != file->ucontext ||
-	    !rcq || rcq->uobject->context != file->ucontext ||
-	    (cmd.is_srq && (!srq || srq->uobject->context != file->ucontext))) {
+	if (!pd || !scq || !rcq || (cmd.is_srq && !srq)) {
 		ret = -EINVAL;
-		goto err_up;
+		goto err_put;
 	}
 
 	attr.event_handler = ib_uverbs_qp_event_handler;
···
 	attr.cap.max_recv_sge    = cmd.max_recv_sge;
 	attr.cap.max_inline_data = cmd.max_inline_data;
 
-	uobj->uevent.uobject.user_handle = cmd.user_handle;
-	uobj->uevent.uobject.context     = file->ucontext;
-	uobj->uevent.events_reported     = 0;
-	INIT_LIST_HEAD(&uobj->uevent.event_list);
-	INIT_LIST_HEAD(&uobj->mcast_list);
+	obj->uevent.events_reported     = 0;
+	INIT_LIST_HEAD(&obj->uevent.event_list);
+	INIT_LIST_HEAD(&obj->mcast_list);
 
 	qp = pd->device->create_qp(pd, &attr, &udata);
 	if (IS_ERR(qp)) {
 		ret = PTR_ERR(qp);
-		goto err_up;
+		goto err_put;
 	}
 
 	qp->device     	  = pd->device;
···
 	qp->send_cq    	  = attr.send_cq;
 	qp->recv_cq    	  = attr.recv_cq;
 	qp->srq	       	  = attr.srq;
-	qp->uobject       = &uobj->uevent.uobject;
+	qp->uobject       = &obj->uevent.uobject;
 	qp->event_handler = attr.event_handler;
 	qp->qp_context    = attr.qp_context;
 	qp->qp_type	  = attr.qp_type;
···
 	if (attr.srq)
 		atomic_inc(&attr.srq->usecnt);
 
-	memset(&resp, 0, sizeof resp);
-	resp.qpn = qp->qp_num;
-
-	ret = idr_add_uobj(&ib_uverbs_qp_idr, qp, &uobj->uevent.uobject);
+	obj->uevent.uobject.object = qp;
+	ret = idr_add_uobj(&ib_uverbs_qp_idr, &obj->uevent.uobject);
 	if (ret)
 		goto err_destroy;
 
-	resp.qp_handle       = uobj->uevent.uobject.id;
+	memset(&resp, 0, sizeof resp);
+	resp.qpn             = qp->qp_num;
+	resp.qp_handle       = obj->uevent.uobject.id;
 	resp.max_recv_sge    = attr.cap.max_recv_sge;
 	resp.max_send_sge    = attr.cap.max_send_sge;
 	resp.max_recv_wr     = attr.cap.max_recv_wr;
···
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp)) {
 		ret = -EFAULT;
-		goto err_idr;
+		goto err_copy;
 	}
 
+	put_pd_read(pd);
+	put_cq_read(scq);
+	put_cq_read(rcq);
+	if (srq)
+		put_srq_read(srq);
+
 	mutex_lock(&file->mutex);
-	list_add_tail(&uobj->uevent.uobject.list, &file->ucontext->qp_list);
+	list_add_tail(&obj->uevent.uobject.list, &file->ucontext->qp_list);
 	mutex_unlock(&file->mutex);
 
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	obj->uevent.uobject.live = 1;
+
+	up_write(&obj->uevent.uobject.mutex);
 
 	return in_len;
 
-err_idr:
-	idr_remove(&ib_uverbs_qp_idr, uobj->uevent.uobject.id);
+err_copy:
+	idr_remove_uobj(&ib_uverbs_qp_idr, &obj->uevent.uobject);
 
 err_destroy:
 	ib_destroy_qp(qp);
 
-err_up:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+err_put:
+	if (pd)
+		put_pd_read(pd);
+	if (scq)
+		put_cq_read(scq);
+	if (rcq)
+		put_cq_read(rcq);
+	if (srq)
+		put_srq_read(srq);
 
-	kfree(uobj);
+	put_uobj_write(&obj->uevent.uobject);
 	return ret;
 }
 
···
 		goto out;
 	}
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	qp = idr_find(&ib_uverbs_qp_idr, cmd.qp_handle);
-	if (qp && qp->uobject->context == file->ucontext)
-		ret = ib_query_qp(qp, attr, cmd.attr_mask, init_attr);
-	else
+	qp = idr_read_qp(cmd.qp_handle, file->ucontext);
+	if (!qp) {
 		ret = -EINVAL;
+		goto out;
+	}
 
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	ret = ib_query_qp(qp, attr, cmd.attr_mask, init_attr);
+
+	put_qp_read(qp);
 
 	if (ret)
 		goto out;
···
 	if (!attr)
 		return -ENOMEM;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	qp = idr_find(&ib_uverbs_qp_idr, cmd.qp_handle);
-	if (!qp || qp->uobject->context != file->ucontext) {
+	qp = idr_read_qp(cmd.qp_handle, file->ucontext);
+	if (!qp) {
 		ret = -EINVAL;
 		goto out;
 	}
···
 	attr->alt_ah_attr.port_num 	    = cmd.alt_dest.port_num;
 
 	ret = ib_modify_qp(qp, attr, cmd.attr_mask);
+
+	put_qp_read(qp);
+
 	if (ret)
 		goto out;
 
 	ret = in_len;
 
 out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
 	kfree(attr);
 
 	return ret;
···
 {
 	struct ib_uverbs_destroy_qp      cmd;
 	struct ib_uverbs_destroy_qp_resp resp;
+	struct ib_uobject		*uobj;
 	struct ib_qp               	*qp;
-	struct ib_uqp_object        	*uobj;
+	struct ib_uqp_object        	*obj;
 	int                        	 ret = -EINVAL;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
···
 
 	memset(&resp, 0, sizeof resp);
 
-	mutex_lock(&ib_uverbs_idr_mutex);
+	uobj = idr_write_uobj(&ib_uverbs_qp_idr, cmd.qp_handle, file->ucontext);
+	if (!uobj)
+		return -EINVAL;
+	qp  = uobj->object;
+	obj = container_of(uobj, struct ib_uqp_object, uevent.uobject);
 
-	qp = idr_find(&ib_uverbs_qp_idr, cmd.qp_handle);
-	if (!qp || qp->uobject->context != file->ucontext)
-		goto out;
-
-	uobj = container_of(qp->uobject, struct ib_uqp_object, uevent.uobject);
-
-	if (!list_empty(&uobj->mcast_list)) {
-		ret = -EBUSY;
-		goto out;
+	if (!list_empty(&obj->mcast_list)) {
+		put_uobj_write(uobj);
+		return -EBUSY;
 	}
 
 	ret = ib_destroy_qp(qp);
-	if (ret)
-		goto out;
+	if (!ret)
+		uobj->live = 0;
 
-	idr_remove(&ib_uverbs_qp_idr, cmd.qp_handle);
+	put_uobj_write(uobj);
+
+	if (ret)
+		return ret;
+
+	idr_remove_uobj(&ib_uverbs_qp_idr, uobj);
 
 	mutex_lock(&file->mutex);
-	list_del(&uobj->uevent.uobject.list);
+	list_del(&uobj->list);
 	mutex_unlock(&file->mutex);
 
-	ib_uverbs_release_uevent(file, &uobj->uevent);
+	ib_uverbs_release_uevent(file, &obj->uevent);
 
-	resp.events_reported = uobj->uevent.events_reported;
+	resp.events_reported = obj->uevent.events_reported;
 
-	kfree(uobj);
+	put_uobj(uobj);
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp))
-		ret = -EFAULT;
+		return -EFAULT;
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
-
-	return ret ? ret : in_len;
+	return in_len;
 }
 
 ssize_t ib_uverbs_post_send(struct ib_uverbs_file *file,
···
 	struct ib_send_wr              *wr = NULL, *last, *next, *bad_wr;
 	struct ib_qp                   *qp;
 	int                             i, sg_ind;
+	int				is_ud;
 	ssize_t                         ret = -EINVAL;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
···
 	if (!user_wr)
 		return -ENOMEM;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	qp = idr_find(&ib_uverbs_qp_idr, cmd.qp_handle);
-	if (!qp || qp->uobject->context != file->ucontext)
+	qp = idr_read_qp(cmd.qp_handle, file->ucontext);
+	if (!qp)
 		goto out;
 
+	is_ud = qp->qp_type == IB_QPT_UD;
 	sg_ind = 0;
 	last = NULL;
 	for (i = 0; i < cmd.wr_count; ++i) {
···
 				   buf + sizeof cmd + i * cmd.wqe_size,
 				   cmd.wqe_size)) {
 			ret = -EFAULT;
-			goto out;
+			goto out_put;
 		}
 
 		if (user_wr->num_sge + sg_ind > cmd.sge_count) {
 			ret = -EINVAL;
-			goto out;
+			goto out_put;
 		}
 
 		next = kmalloc(ALIGN(sizeof *next, sizeof (struct ib_sge)) +
···
 			       GFP_KERNEL);
 		if (!next) {
 			ret = -ENOMEM;
-			goto out;
+			goto out_put;
 		}
 
 		if (!last)
···
 		next->send_flags = user_wr->send_flags;
 		next->imm_data   = (__be32 __force) user_wr->imm_data;
 
-		if (qp->qp_type == IB_QPT_UD) {
-			next->wr.ud.ah = idr_find(&ib_uverbs_ah_idr,
-						  user_wr->wr.ud.ah);
+		if (is_ud) {
+			next->wr.ud.ah = idr_read_ah(user_wr->wr.ud.ah,
+						     file->ucontext);
 			if (!next->wr.ud.ah) {
 				ret = -EINVAL;
-				goto out;
+				goto out_put;
 			}
 			next->wr.ud.remote_qpn  = user_wr->wr.ud.remote_qpn;
 			next->wr.ud.remote_qkey = user_wr->wr.ud.remote_qkey;
···
 					   sg_ind * sizeof (struct ib_sge),
 					   next->num_sge * sizeof (struct ib_sge))) {
 				ret = -EFAULT;
-				goto out;
+				goto out_put;
 			}
 			sg_ind += next->num_sge;
 		} else
···
 			 &resp, sizeof resp))
 		ret = -EFAULT;
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+out_put:
+	put_qp_read(qp);
 
+out:
 	while (wr) {
+		if (is_ud && wr->wr.ud.ah)
+			put_ah_read(wr->wr.ud.ah);
 		next = wr->next;
 		kfree(wr);
 		wr = next;
···
 	if (IS_ERR(wr))
 		return PTR_ERR(wr);
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	qp = idr_find(&ib_uverbs_qp_idr, cmd.qp_handle);
-	if (!qp || qp->uobject->context != file->ucontext)
+	qp = idr_read_qp(cmd.qp_handle, file->ucontext);
+	if (!qp)
 		goto out;
 
 	resp.bad_wr = 0;
 	ret = qp->device->post_recv(qp, wr, &bad_wr);
+
+	put_qp_read(qp);
+
 	if (ret)
 		for (next = wr; next; next = next->next) {
 			++resp.bad_wr;
···
 		ret = -EFAULT;
 
 out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
-
 	while (wr) {
 		next = wr->next;
 		kfree(wr);
···
 	if (IS_ERR(wr))
 		return PTR_ERR(wr);
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	srq = idr_find(&ib_uverbs_srq_idr, cmd.srq_handle);
-	if (!srq || srq->uobject->context != file->ucontext)
+	srq = idr_read_srq(cmd.srq_handle, file->ucontext);
+	if (!srq)
 		goto out;
 
 	resp.bad_wr = 0;
 	ret = srq->device->post_srq_recv(srq, wr, &bad_wr);
+
+	put_srq_read(srq);
+
 	if (ret)
 		for (next = wr; next; next = next->next) {
 			++resp.bad_wr;
···
 		ret = -EFAULT;
 
 out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
-
 	while (wr) {
 		next = wr->next;
 		kfree(wr);
···
 	if (!uobj)
 		return -ENOMEM;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
+	init_uobj(uobj, cmd.user_handle, file->ucontext);
+	down_write(&uobj->mutex);
 
-	pd = idr_find(&ib_uverbs_pd_idr, cmd.pd_handle);
-	if (!pd || pd->uobject->context != file->ucontext) {
+	pd = idr_read_pd(cmd.pd_handle, file->ucontext);
+	if (!pd) {
 		ret = -EINVAL;
-		goto err_up;
+		goto err;
 	}
-
-	uobj->user_handle = cmd.user_handle;
-	uobj->context     = file->ucontext;
 
 	attr.dlid 	       = cmd.attr.dlid;
 	attr.sl 	       = cmd.attr.sl;
···
 	ah = ib_create_ah(pd, &attr);
 	if (IS_ERR(ah)) {
 		ret = PTR_ERR(ah);
-		goto err_up;
+		goto err;
 	}
 
-	ah->uobject = uobj;
+	ah->uobject  = uobj;
+	uobj->object = ah;
 
-	ret = idr_add_uobj(&ib_uverbs_ah_idr, ah, uobj);
+	ret = idr_add_uobj(&ib_uverbs_ah_idr, uobj);
 	if (ret)
 		goto err_destroy;
 
···
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp)) {
 		ret = -EFAULT;
-		goto err_idr;
+		goto err_copy;
 	}
+
+	put_pd_read(pd);
 
 	mutex_lock(&file->mutex);
 	list_add_tail(&uobj->list, &file->ucontext->ah_list);
 	mutex_unlock(&file->mutex);
 
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	uobj->live = 1;
+
+	up_write(&uobj->mutex);
 
 	return in_len;
 
-err_idr:
-	idr_remove(&ib_uverbs_ah_idr, uobj->id);
+err_copy:
+	idr_remove_uobj(&ib_uverbs_ah_idr, uobj);
 
 err_destroy:
 	ib_destroy_ah(ah);
 
-err_up:
-	mutex_unlock(&ib_uverbs_idr_mutex);
-
-	kfree(uobj);
+err:
+	put_uobj_write(uobj);
 	return ret;
 }
 
···
 	struct ib_uverbs_destroy_ah cmd;
 	struct ib_ah		   *ah;
 	struct ib_uobject	   *uobj;
-	int			    ret = -EINVAL;
+	int			    ret;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	ah = idr_find(&ib_uverbs_ah_idr, cmd.ah_handle);
-	if (!ah || ah->uobject->context != file->ucontext)
-		goto out;
-
-	uobj = ah->uobject;
+	uobj = idr_write_uobj(&ib_uverbs_ah_idr, cmd.ah_handle, file->ucontext);
+	if (!uobj)
+		return -EINVAL;
+	ah = uobj->object;
 
 	ret = ib_destroy_ah(ah);
-	if (ret)
-		goto out;
+	if (!ret)
+		uobj->live = 0;
 
-	idr_remove(&ib_uverbs_ah_idr, cmd.ah_handle);
+	put_uobj_write(uobj);
+
+	if (ret)
+		return ret;
+
+	idr_remove_uobj(&ib_uverbs_ah_idr, uobj);
 
 	mutex_lock(&file->mutex);
 	list_del(&uobj->list);
 	mutex_unlock(&file->mutex);
 
-	kfree(uobj);
+	put_uobj(uobj);
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
-
-	return ret ? ret : in_len;
+	return in_len;
 }
 
 ssize_t ib_uverbs_attach_mcast(struct ib_uverbs_file *file,
···
 {
 	struct ib_uverbs_attach_mcast cmd;
 	struct ib_qp                 *qp;
-	struct ib_uqp_object         *uobj;
+	struct ib_uqp_object         *obj;
 	struct ib_uverbs_mcast_entry *mcast;
-	int                           ret = -EINVAL;
+	int                           ret;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
+	qp = idr_read_qp(cmd.qp_handle, file->ucontext);
+	if (!qp)
+		return -EINVAL;
 
-	qp = idr_find(&ib_uverbs_qp_idr, cmd.qp_handle);
-	if (!qp || qp->uobject->context != file->ucontext)
-		goto out;
+	obj = container_of(qp->uobject, struct ib_uqp_object, uevent.uobject);
 
-	uobj = container_of(qp->uobject, struct ib_uqp_object, uevent.uobject);
-
-	list_for_each_entry(mcast, &uobj->mcast_list, list)
+	list_for_each_entry(mcast, &obj->mcast_list, list)
 		if (cmd.mlid == mcast->lid &&
 		    !memcmp(cmd.gid, mcast->gid.raw, sizeof mcast->gid.raw)) {
 			ret = 0;
-			goto out;
+			goto out_put;
 		}
 
 	mcast = kmalloc(sizeof *mcast, GFP_KERNEL);
 	if (!mcast) {
 		ret = -ENOMEM;
-		goto out;
+		goto out_put;
 	}
 
 	mcast->lid = cmd.mlid;
 	memcpy(mcast->gid.raw, cmd.gid, sizeof mcast->gid.raw);
 
 	ret = ib_attach_mcast(qp, &mcast->gid, cmd.mlid);
-	if (!ret) {
-		uobj = container_of(qp->uobject, struct ib_uqp_object,
-				    uevent.uobject);
-		list_add_tail(&mcast->list, &uobj->mcast_list);
-	} else
+	if (!ret)
+		list_add_tail(&mcast->list, &obj->mcast_list);
+	else
 		kfree(mcast);
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+out_put:
+	put_qp_read(qp);
 
 	return ret ? ret : in_len;
 }
···
 			       int out_len)
 {
 	struct ib_uverbs_detach_mcast cmd;
-	struct ib_uqp_object         *uobj;
+	struct ib_uqp_object         *obj;
 	struct ib_qp                 *qp;
 	struct ib_uverbs_mcast_entry *mcast;
 	int                           ret = -EINVAL;
···
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	qp = idr_find(&ib_uverbs_qp_idr, cmd.qp_handle);
-	if (!qp || qp->uobject->context != file->ucontext)
-		goto out;
+	qp = idr_read_qp(cmd.qp_handle, file->ucontext);
+	if (!qp)
+		return -EINVAL;
 
 	ret = ib_detach_mcast(qp, (union ib_gid *) cmd.gid, cmd.mlid);
 	if (ret)
-		goto out;
+		goto out_put;
 
-	uobj = container_of(qp->uobject, struct ib_uqp_object, uevent.uobject);
+	obj = container_of(qp->uobject, struct ib_uqp_object, uevent.uobject);
 
-	list_for_each_entry(mcast, &uobj->mcast_list, list)
+	list_for_each_entry(mcast, &obj->mcast_list, list)
 		if (cmd.mlid == mcast->lid &&
 		    !memcmp(cmd.gid, mcast->gid.raw, sizeof mcast->gid.raw)) {
 			list_del(&mcast->list);
···
 			break;
 		}
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+out_put:
+	put_qp_read(qp);
 
 	return ret ? ret : in_len;
 }
···
 	struct ib_uverbs_create_srq      cmd;
 	struct ib_uverbs_create_srq_resp resp;
 	struct ib_udata                  udata;
-	struct ib_uevent_object         *uobj;
+	struct ib_uevent_object         *obj;
 	struct ib_pd                    *pd;
 	struct ib_srq                   *srq;
 	struct ib_srq_init_attr          attr;
···
 		   (unsigned long) cmd.response + sizeof resp,
 		   in_len - sizeof cmd, out_len - sizeof resp);
 
-	uobj = kmalloc(sizeof *uobj, GFP_KERNEL);
-	if (!uobj)
+	obj = kmalloc(sizeof *obj, GFP_KERNEL);
+	if (!obj)
 		return -ENOMEM;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
+	init_uobj(&obj->uobject, 0, file->ucontext);
+	down_write(&obj->uobject.mutex);
 
-	pd  = idr_find(&ib_uverbs_pd_idr, cmd.pd_handle);
-
-	if (!pd || pd->uobject->context != file->ucontext) {
+	pd  = idr_read_pd(cmd.pd_handle, file->ucontext);
+	if (!pd) {
 		ret = -EINVAL;
-		goto err_up;
+		goto err;
 	}
 
 	attr.event_handler  = ib_uverbs_srq_event_handler;
···
 	attr.attr.max_sge   = cmd.max_sge;
 	attr.attr.srq_limit = cmd.srq_limit;
 
-	uobj->uobject.user_handle = cmd.user_handle;
-	uobj->uobject.context     = file->ucontext;
-	uobj->events_reported     = 0;
-	INIT_LIST_HEAD(&uobj->event_list);
+	obj->events_reported     = 0;
+	INIT_LIST_HEAD(&obj->event_list);
 
 	srq = pd->device->create_srq(pd, &attr, &udata);
 	if (IS_ERR(srq)) {
 		ret = PTR_ERR(srq);
-		goto err_up;
+		goto err;
 	}
 
 	srq->device    	   = pd->device;
 	srq->pd        	   = pd;
-	srq->uobject       = &uobj->uobject;
+	srq->uobject       = &obj->uobject;
 	srq->event_handler = attr.event_handler;
 	srq->srq_context   = attr.srq_context;
 	atomic_inc(&pd->usecnt);
 	atomic_set(&srq->usecnt, 0);
 
-	memset(&resp, 0, sizeof resp);
-
-	ret = idr_add_uobj(&ib_uverbs_srq_idr, srq, &uobj->uobject);
+	obj->uobject.object = srq;
+	ret = idr_add_uobj(&ib_uverbs_srq_idr, &obj->uobject);
 	if (ret)
 		goto err_destroy;
 
-	resp.srq_handle = uobj->uobject.id;
+	memset(&resp, 0, sizeof resp);
+	resp.srq_handle = obj->uobject.id;
 	resp.max_wr     = attr.attr.max_wr;
 	resp.max_sge    = attr.attr.max_sge;
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp)) {
 		ret = -EFAULT;
-		goto err_idr;
+		goto err_copy;
 	}
 
+	put_pd_read(pd);
+
 	mutex_lock(&file->mutex);
-	list_add_tail(&uobj->uobject.list, &file->ucontext->srq_list);
+	list_add_tail(&obj->uobject.list, &file->ucontext->srq_list);
 	mutex_unlock(&file->mutex);
 
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	obj->uobject.live = 1;
+
+	up_write(&obj->uobject.mutex);
 
 	return in_len;
 
-err_idr:
-	idr_remove(&ib_uverbs_srq_idr, uobj->uobject.id);
+err_copy:
+	idr_remove_uobj(&ib_uverbs_srq_idr, &obj->uobject);
 
 err_destroy:
 	ib_destroy_srq(srq);
 
-err_up:
-	mutex_unlock(&ib_uverbs_idr_mutex);
-
-	kfree(uobj);
+err:
+	put_uobj_write(&obj->uobject);
 	return ret;
 }
 
···
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	srq = idr_find(&ib_uverbs_srq_idr, cmd.srq_handle);
-	if (!srq || srq->uobject->context != file->ucontext) {
-		ret = -EINVAL;
-		goto out;
-	}
+	srq = idr_read_srq(cmd.srq_handle, file->ucontext);
+	if (!srq)
+		return -EINVAL;
 
 	attr.max_wr    = cmd.max_wr;
 	attr.srq_limit = cmd.srq_limit;
 
 	ret = ib_modify_srq(srq, &attr, cmd.attr_mask);
 
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	put_srq_read(srq);
 
 	return ret ? ret : in_len;
 }
···
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
+	srq = idr_read_srq(cmd.srq_handle, file->ucontext);
+	if (!srq)
+		return -EINVAL;
 
-	srq = idr_find(&ib_uverbs_srq_idr, cmd.srq_handle);
-	if (srq && srq->uobject->context == file->ucontext)
-		ret = ib_query_srq(srq, &attr);
-	else
-		ret = -EINVAL;
+	ret = ib_query_srq(srq, &attr);
 
-	mutex_unlock(&ib_uverbs_idr_mutex);
+	put_srq_read(srq);
 
 	if (ret)
-		goto out;
+		return ret;
 
 	memset(&resp, 0, sizeof resp);
 
···
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp))
-		ret = -EFAULT;
+		return -EFAULT;
 
-out:
-	return ret ? ret : in_len;
+	return in_len;
 }
 
 ssize_t ib_uverbs_destroy_srq(struct ib_uverbs_file *file,
···
 {
 	struct ib_uverbs_destroy_srq      cmd;
 	struct ib_uverbs_destroy_srq_resp resp;
+	struct ib_uobject		 *uobj;
 	struct ib_srq               	 *srq;
-	struct ib_uevent_object        	 *uobj;
+	struct ib_uevent_object        	 *obj;
 	int                         	  ret = -EINVAL;
 
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
-	memset(&resp, 0, sizeof resp);
-
-	srq = idr_find(&ib_uverbs_srq_idr, cmd.srq_handle);
-	if (!srq || srq->uobject->context != file->ucontext)
-		goto out;
-
-	uobj = container_of(srq->uobject, struct ib_uevent_object, uobject);
+	uobj = idr_write_uobj(&ib_uverbs_srq_idr, cmd.srq_handle, file->ucontext);
+	if (!uobj)
+		return -EINVAL;
+	srq = uobj->object;
+	obj = container_of(uobj, struct ib_uevent_object, uobject);
 
 	ret = ib_destroy_srq(srq);
-	if (ret)
-		goto out;
+	if (!ret)
+		uobj->live = 0;
 
-	idr_remove(&ib_uverbs_srq_idr, cmd.srq_handle);
+	put_uobj_write(uobj);
+
+	if (ret)
+		return ret;
+
+	idr_remove_uobj(&ib_uverbs_srq_idr, uobj);
 
 	mutex_lock(&file->mutex);
-	list_del(&uobj->uobject.list);
+	list_del(&uobj->list);
 	mutex_unlock(&file->mutex);
 
-	ib_uverbs_release_uevent(file, uobj);
+	ib_uverbs_release_uevent(file, obj);
 
-	resp.events_reported = uobj->events_reported;
+	memset(&resp, 0, sizeof resp);
+	resp.events_reported = obj->events_reported;
 
-	kfree(uobj);
+	put_uobj(uobj);
 
 	if (copy_to_user((void __user *) (unsigned long) cmd.response,
 			 &resp, sizeof resp))
 		ret = -EFAULT;
-
-out:
-	mutex_unlock(&ib_uverbs_idr_mutex);
 
 	return ret ? ret : in_len;
 }

drivers/infiniband/core/uverbs_main.c

···
 
 static struct class *uverbs_class;
 
-DEFINE_MUTEX(ib_uverbs_idr_mutex);
+DEFINE_SPINLOCK(ib_uverbs_idr_lock);
 DEFINE_IDR(ib_uverbs_pd_idr);
 DEFINE_IDR(ib_uverbs_mr_idr);
 DEFINE_IDR(ib_uverbs_mw_idr);
···
 	if (!context)
 		return 0;
 
-	mutex_lock(&ib_uverbs_idr_mutex);
-
 	list_for_each_entry_safe(uobj, tmp, &context->ah_list, list) {
-		struct ib_ah *ah = idr_find(&ib_uverbs_ah_idr, uobj->id);
-		idr_remove(&ib_uverbs_ah_idr, uobj->id);
+		struct ib_ah *ah = uobj->object;
+
+		idr_remove_uobj(&ib_uverbs_ah_idr, uobj);
 		ib_destroy_ah(ah);
 		list_del(&uobj->list);
 		kfree(uobj);
 	}
 
 	list_for_each_entry_safe(uobj, tmp, &context->qp_list, list) {
-		struct ib_qp *qp = idr_find(&ib_uverbs_qp_idr, uobj->id);
+		struct ib_qp *qp = uobj->object;
 		struct ib_uqp_object *uqp =
 			container_of(uobj, struct ib_uqp_object, uevent.uobject);
-		idr_remove(&ib_uverbs_qp_idr, uobj->id);
+
+		idr_remove_uobj(&ib_uverbs_qp_idr, uobj);
 		ib_uverbs_detach_umcast(qp, uqp);
 		ib_destroy_qp(qp);
 		list_del(&uobj->list);
···
 	}
 
 	list_for_each_entry_safe(uobj, tmp, &context->cq_list, list) {
-		struct ib_cq *cq = idr_find(&ib_uverbs_cq_idr, uobj->id);
+		struct ib_cq *cq = uobj->object;
 		struct ib_uverbs_event_file *ev_file = cq->cq_context;
 		struct ib_ucq_object *ucq =
 			container_of(uobj, struct ib_ucq_object, uobject);
-		idr_remove(&ib_uverbs_cq_idr, uobj->id);
+
+		idr_remove_uobj(&ib_uverbs_cq_idr, uobj);
 		ib_destroy_cq(cq);
 		list_del(&uobj->list);
 		ib_uverbs_release_ucq(file, ev_file, ucq);
···
 	}
 
 	list_for_each_entry_safe(uobj, tmp, &context->srq_list, list) {
-		struct ib_srq *srq = idr_find(&ib_uverbs_srq_idr, uobj->id);
+		struct ib_srq *srq = uobj->object;
 		struct ib_uevent_object *uevent =
 			container_of(uobj, struct ib_uevent_object, uobject);
-		idr_remove(&ib_uverbs_srq_idr, uobj->id);
+
+		idr_remove_uobj(&ib_uverbs_srq_idr, uobj);
 		ib_destroy_srq(srq);
 		list_del(&uobj->list);
 		ib_uverbs_release_uevent(file, uevent);
···
 	/* XXX Free MWs */
 
 	list_for_each_entry_safe(uobj, tmp, &context->mr_list, list) {
-		struct ib_mr *mr = idr_find(&ib_uverbs_mr_idr, uobj->id);
+		struct ib_mr *mr = uobj->object;
 		struct ib_device *mrdev = mr->device;
 		struct ib_umem_object *memobj;
 
-		idr_remove(&ib_uverbs_mr_idr, uobj->id);
+		idr_remove_uobj(&ib_uverbs_mr_idr, uobj);
 		ib_dereg_mr(mr);
 
 		memobj = container_of(uobj, struct ib_umem_object, uobject);
···
 	}
 
 	list_for_each_entry_safe(uobj, tmp, &context->pd_list, list) {
-		struct ib_pd *pd = idr_find(&ib_uverbs_pd_idr, uobj->id);
-		idr_remove(&ib_uverbs_pd_idr, uobj->id);
+		struct ib_pd *pd = uobj->object;
+
+		idr_remove_uobj(&ib_uverbs_pd_idr, uobj);
 		ib_dealloc_pd(pd);
 		list_del(&uobj->list);
 		kfree(uobj);
 	}
-
-	mutex_unlock(&ib_uverbs_idr_mutex);
 
 	return context->device->dealloc_ucontext(context);
 }

include/rdma/ib_verbs.h

···
 struct ib_uobject {
 	u64			user_handle;	/* handle given to us by userspace */
 	struct ib_ucontext     *context;	/* associated user context */
+	void		       *object;		/* containing object */
 	struct list_head	list;		/* link to context's list */
 	u32			id;		/* index into kernel idr */
+	struct kref		ref;
+	struct rw_semaphore	mutex;		/* protects .live */
+	int			live;
 };
 
 struct ib_umem {