IB/uverbs: Revise and clarify the rwsem and uobjects_lock

Rename 'cleanup_rwsem' to 'hw_destroy_rwsem' which is held across any call
to the type destroy function (aka 'hw' destroy). The main purpose of this
lock is to prevent normal add and destroy from running concurrently with
uverbs_cleanup_ufile()

Since the uobjects list is always manipulated under the 'hw_destroy_rwsem'
we can eliminate the uobjects_lock in the cleanup function. This allows
converting that lock to a very simple spinlock with a narrow critical
section.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

1 files changed, 12 insertions, 14 deletions

diff --git a/drivers/infiniband/core/rdma_core.c b/drivers/infiniband/core/rdma_core.c
index a55646cbf9b1..4545c661acaa 100644
--- a/drivers/infiniband/core/rdma_core.c
+++ b/drivers/infiniband/core/rdma_core.c
@@ -461,9 +461,9 @@ static int __must_check _rdma_remove_commit_uobject(struct ib_uobject *uobj,
 
 	uobj->object = NULL;
 
-	mutex_lock(&ufile->uobjects_lock);
+	spin_lock_irq(&ufile->uobjects_lock);
 	list_del(&uobj->list);
-	mutex_unlock(&ufile->uobjects_lock);
+	spin_unlock_irq(&ufile->uobjects_lock);
 	/* Pairs with the get in rdma_alloc_commit_uobject() */
 	uverbs_uobject_put(uobj);
 
@@ -491,14 +491,14 @@ int rdma_explicit_destroy(struct ib_uobject *uobject)
 	struct ib_uverbs_file *ufile = uobject->ufile;
 
 	/* Cleanup is running. Calling this should have been impossible */
-	if (!down_read_trylock(&ufile->cleanup_rwsem)) {
+	if (!down_read_trylock(&ufile->hw_destroy_rwsem)) {
 		WARN(true, "ib_uverbs: Cleanup is running while removing an uobject\n");
 		return 0;
 	}
 	assert_uverbs_usecnt(uobject, true);
 	ret = _rdma_remove_commit_uobject(uobject, RDMA_REMOVE_DESTROY);
 
-	up_read(&ufile->cleanup_rwsem);
+	up_read(&ufile->hw_destroy_rwsem);
 	return ret;
 }
 
@@ -541,7 +541,7 @@ int rdma_alloc_commit_uobject(struct ib_uobject *uobj)
 	struct ib_uverbs_file *ufile = uobj->ufile;
 
 	/* Cleanup is running. Calling this should have been impossible */
-	if (!down_read_trylock(&ufile->cleanup_rwsem)) {
+	if (!down_read_trylock(&ufile->hw_destroy_rwsem)) {
 		int ret;
 
 		WARN(true, "ib_uverbs: Cleanup is running while allocating an uobject\n");
@@ -559,13 +559,13 @@ int rdma_alloc_commit_uobject(struct ib_uobject *uobj)
 
 	/* kref is held so long as the uobj is on the uobj list. */
 	uverbs_uobject_get(uobj);
-	mutex_lock(&ufile->uobjects_lock);
+	spin_lock_irq(&ufile->uobjects_lock);
 	list_add(&uobj->list, &ufile->uobjects);
-	mutex_unlock(&ufile->uobjects_lock);
+	spin_unlock_irq(&ufile->uobjects_lock);
 
 	/* alloc_commit consumes the uobj kref */
 	uobj->type->type_class->alloc_commit(uobj);
-	up_read(&ufile->cleanup_rwsem);
+	up_read(&ufile->hw_destroy_rwsem);
 
 	return 0;
 }
@@ -681,9 +681,9 @@ void uverbs_close_fd(struct file *f)
 	struct ib_uobject *uobj = f->private_data;
 	struct ib_uverbs_file *ufile = uobj->ufile;
 
-	if (down_read_trylock(&ufile->cleanup_rwsem)) {
+	if (down_read_trylock(&ufile->hw_destroy_rwsem)) {
 		_uverbs_close_fd(uobj);
-		up_read(&ufile->cleanup_rwsem);
+		up_read(&ufile->hw_destroy_rwsem);
 	}
 
 	uobj->object = NULL;
@@ -710,7 +710,6 @@ static int __uverbs_cleanup_ufile(struct ib_uverbs_file *ufile,
 	 * We take and release the lock per traversal in order to let
 	 * other threads (which might still use the FDs) chance to run.
 	 */
-	mutex_lock(&ufile->uobjects_lock);
 	ufile->cleanup_reason = reason;
 	list_for_each_entry_safe(obj, next_obj, &ufile->uobjects, list) {
 		/*
@@ -736,7 +735,6 @@ static int __uverbs_cleanup_ufile(struct ib_uverbs_file *ufile,
 		uverbs_uobject_put(obj);
 		ret = 0;
 	}
-	mutex_unlock(&ufile->uobjects_lock);
 	return ret;
 }
 
@@ -751,7 +749,7 @@ void uverbs_cleanup_ufile(struct ib_uverbs_file *ufile, bool device_removed)
 	 * want to hold this forever as the context is going to be destroyed,
 	 * but we'll release it since it causes a "held lock freed" BUG message.
 	 */
-	down_write(&ufile->cleanup_rwsem);
+	down_write(&ufile->hw_destroy_rwsem);
 	ufile->ucontext->cleanup_retryable = true;
 	while (!list_empty(&ufile->uobjects))
 		if (__uverbs_cleanup_ufile(ufile, reason)) {
@@ -766,7 +764,7 @@ void uverbs_cleanup_ufile(struct ib_uverbs_file *ufile, bool device_removed)
 	if (!list_empty(&ufile->uobjects))
 		__uverbs_cleanup_ufile(ufile, reason);
 
-	up_write(&ufile->cleanup_rwsem);
+	up_write(&ufile->hw_destroy_rwsem);
 }
 
 const struct uverbs_obj_type_class uverbs_fd_class = {