[PATCH rdma-next 1/8] RDMA/core: Add rdma_restrack_begin/abort/commit_del() operations

[Edward Srouji <edwards@nvidia.com>]

From: Patrisious Haddad <phaddad@nvidia.com>

Add rdma_restrack_abort_del(), rdma_restrack_begin_del() and
rdma_restrack_commit_del() functions to allow deleting a resource from
the xarray to effectively prevent future access to it and wait for all
current users to finish while preserving its index in the xarray to
allow to re-insert it if needed with guaranteed success.

This is a preparatory change for subsequent patches in the series
which will use these functions to fix the cleanup flow.

Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
---
 drivers/infiniband/core/restrack.c | 167 +++++++++++++++++++++++++++++--------
 drivers/infiniband/core/restrack.h |   3 +
 2 files changed, 137 insertions(+), 33 deletions(-)

diff --git a/drivers/infiniband/core/restrack.c b/drivers/infiniband/core/restrack.c
index cfee2071586c16e3dfc4e21e5d58f8488dfb277f..30d433ee79a042fe270c9ed2f47b0e2d4a388ff9 100644
--- a/drivers/infiniband/core/restrack.c
+++ b/drivers/infiniband/core/restrack.c
@@ -129,6 +129,40 @@ static void rdma_restrack_attach_task(struct rdma_restrack_entry *res,
 	res->user = true;
 }
 
+static struct rdma_restrack_root *res_to_rt(struct rdma_restrack_entry *res)
+{
+	struct ib_device *dev = res_to_dev(res);
+
+	if (WARN_ON(!dev))
+		return NULL;
+
+	return &dev->res[res->type];
+}
+
+static void restrack_drain_res(struct rdma_restrack_root *rt,
+			       struct rdma_restrack_entry *res)
+{
+	struct rdma_restrack_entry *old;
+
+	old = xa_cmpxchg(&rt->xa, res->id, res, XA_ZERO_ENTRY, GFP_KERNEL);
+	WARN_ON(old != res);
+
+	rdma_restrack_put(res);
+	wait_for_completion(&res->comp);
+}
+
+static void restrack_restore_res(struct rdma_restrack_root *rt,
+				 struct rdma_restrack_entry *res)
+{
+	struct rdma_restrack_entry *old;
+
+	reinit_completion(&res->comp);
+	kref_init(&res->kref);
+
+	old = xa_cmpxchg(&rt->xa, res->id, XA_ZERO_ENTRY, res, GFP_KERNEL);
+	WARN_ON(old);
+}
+
 /**
  * rdma_restrack_set_name() - set the task for this resource
  * @res:  resource entry
@@ -177,22 +211,23 @@ void rdma_restrack_new(struct rdma_restrack_entry *res,
 EXPORT_SYMBOL(rdma_restrack_new);
 
 /**
- * rdma_restrack_add() - add object to the resource tracking database
+ * rdma_restrack_add() - add object to the resource tracking database.
+ * If this resource reuses an ID of a resource that was already destroyed
+ * after calling rdma_restrack_begin() but didn't yet call
+ * rdma_restrack_commit_del() it can result in an untracked QP.
  * @res:  resource entry
  */
 void rdma_restrack_add(struct rdma_restrack_entry *res)
 {
-	struct ib_device *dev = res_to_dev(res);
 	struct rdma_restrack_root *rt;
 	int ret = 0;
 
-	if (!dev)
-		return;
-
 	if (res->no_track)
 		goto out;
 
-	rt = &dev->res[res->type];
+	rt = res_to_rt(res);
+	if (!rt)
+		return;
 
 	if (res->type == RDMA_RESTRACK_QP) {
 		/* Special case to ensure that LQPN points to right QP */
@@ -229,6 +264,32 @@ void rdma_restrack_add(struct rdma_restrack_entry *res)
 }
 EXPORT_SYMBOL(rdma_restrack_add);
 
+/**
+ * rdma_restrack_abort_del() - re-add object to the resource tracking database
+ * it can only be used after rdma_restrack_begin_del().
+ * @res:  resource entry
+ */
+void rdma_restrack_abort_del(struct rdma_restrack_entry *res)
+{
+	struct rdma_restrack_root *rt;
+
+	if (!res->valid)
+		return;
+
+	if (res->no_track) {
+		reinit_completion(&res->comp);
+		kref_init(&res->kref);
+		return;
+	}
+
+	rt = res_to_rt(res);
+	if (!rt)
+		return;
+
+	restrack_restore_res(rt, res);
+}
+EXPORT_SYMBOL(rdma_restrack_abort_del);
+
 int __must_check rdma_restrack_get(struct rdma_restrack_entry *res)
 {
 	return kref_get_unless_zero(&res->kref);
@@ -265,7 +326,7 @@ static void restrack_release(struct kref *kref)
 	struct rdma_restrack_entry *res;
 
 	res = container_of(kref, struct rdma_restrack_entry, kref);
-	if (res->task) {
+	if (res->task && !res->valid) {
 		put_task_struct(res->task);
 		res->task = NULL;
 	}
@@ -291,37 +352,20 @@ EXPORT_SYMBOL(rdma_restrack_put);
  */
 void rdma_restrack_sync(struct rdma_restrack_entry *res)
 {
-	struct rdma_restrack_entry *old;
 	struct rdma_restrack_root *rt;
-	struct task_struct *task;
-	struct ib_device *dev;
 
 	if (!res->valid || res->no_track)
 		return;
 
-	dev = res_to_dev(res);
-	if (WARN_ON(!dev))
+	rt = res_to_rt(res);
+	if (!rt)
 		return;
 
-	rt = &dev->res[res->type];
 	if (WARN_ON(xa_get_mark(&rt->xa, res->id, RESTRACK_DD)))
 		return;
 
-	old = xa_cmpxchg(&rt->xa, res->id, res, XA_ZERO_ENTRY, GFP_KERNEL);
-	if (WARN_ON(old != res))
-		return;
-
-	task = res->task;
-	if (task)
-		get_task_struct(task);
-	rdma_restrack_put(res);
-	wait_for_completion(&res->comp);
-	reinit_completion(&res->comp);
-	if (task)
-		res->task = task;
-	kref_init(&res->kref);
-
-	xa_cmpxchg(&rt->xa, res->id, XA_ZERO_ENTRY, res, GFP_KERNEL);
+	restrack_drain_res(rt, res);
+	restrack_restore_res(rt, res);
 }
 EXPORT_SYMBOL(rdma_restrack_sync);
 
@@ -333,7 +377,6 @@ void rdma_restrack_del(struct rdma_restrack_entry *res)
 {
 	struct rdma_restrack_entry *old;
 	struct rdma_restrack_root *rt;
-	struct ib_device *dev;
 
 	if (!res->valid) {
 		if (res->task) {
@@ -346,12 +389,10 @@ void rdma_restrack_del(struct rdma_restrack_entry *res)
 	if (res->no_track)
 		goto out;
 
-	dev = res_to_dev(res);
-	if (WARN_ON(!dev))
+	rt = res_to_rt(res);
+	if (!rt)
 		return;
 
-	rt = &dev->res[res->type];
-
 	old = xa_erase(&rt->xa, res->id);
 	WARN_ON(old != res);
 
@@ -359,5 +400,65 @@ void rdma_restrack_del(struct rdma_restrack_entry *res)
 	res->valid = false;
 	rdma_restrack_put(res);
 	wait_for_completion(&res->comp);
+	if (res->task) {
+		put_task_struct(res->task);
+		res->task = NULL;
+	}
 }
 EXPORT_SYMBOL(rdma_restrack_del);
+
+/**
+ * rdma_restrack_begin_del() - invalidate the object from the resource tracking
+ * database but preserve its index in the array.
+ * Since this preserves the index in the array until rdma_restrack_commit_del()
+ * is called, if rdma_restrack_add() is called in between with an old QP ID it
+ * can result in an untracked QP.
+ * @res:  resource entry
+ */
+void rdma_restrack_begin_del(struct rdma_restrack_entry *res)
+{
+	struct rdma_restrack_root *rt;
+
+	if (!res->valid)
+		return;
+
+	if (res->no_track) {
+		rdma_restrack_put(res);
+		wait_for_completion(&res->comp);
+		return;
+	}
+
+	rt = res_to_rt(res);
+	if (!rt)
+		return;
+
+	restrack_drain_res(rt, res);
+}
+EXPORT_SYMBOL(rdma_restrack_begin_del);
+
+/**
+ * rdma_restrack_commit_del() - delete object from the resource tracking
+ * database and free the task.
+ * @res:  resource entry
+ */
+void rdma_restrack_commit_del(struct rdma_restrack_entry *res)
+{
+	struct rdma_restrack_root *rt;
+
+	if (!res->valid || res->no_track)
+		goto out;
+
+	rt = res_to_rt(res);
+	if (!rt)
+		return;
+
+	xa_erase(&rt->xa, res->id);
+
+out:
+	res->valid = false;
+	if (res->task) {
+		put_task_struct(res->task);
+		res->task = NULL;
+	}
+}
+EXPORT_SYMBOL(rdma_restrack_commit_del);
diff --git a/drivers/infiniband/core/restrack.h b/drivers/infiniband/core/restrack.h
index 75b8d1005a984b21896e296ac6ace1415a90905f..2df78e084e107c517a2468982add74ce3562e5f2 100644
--- a/drivers/infiniband/core/restrack.h
+++ b/drivers/infiniband/core/restrack.h
@@ -26,8 +26,11 @@ struct rdma_restrack_root {
 int rdma_restrack_init(struct ib_device *dev);
 void rdma_restrack_clean(struct ib_device *dev);
 void rdma_restrack_add(struct rdma_restrack_entry *res);
+void rdma_restrack_abort_del(struct rdma_restrack_entry *res);
 void rdma_restrack_del(struct rdma_restrack_entry *res);
 void rdma_restrack_sync(struct rdma_restrack_entry *res);
+void rdma_restrack_begin_del(struct rdma_restrack_entry *res);
+void rdma_restrack_commit_del(struct rdma_restrack_entry *res);
 void rdma_restrack_new(struct rdma_restrack_entry *res,
 		       enum rdma_restrack_type type);
 void rdma_restrack_set_name(struct rdma_restrack_entry *res,

-- 
2.49.0