IB/uverbs: Do not block disassociate during write()

Now that all the callbacks are safe to run concurrently with
disassociation this test can be eliminated. The ufile core infrastructure
becomes entirely self contained and is not sensitive to disassociation.
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/uverbs.h

@@ -158,6 +158,9 @@ struct ib_uverbs_file {
 	spinlock_t		uobjects_lock;
 	struct list_head	uobjects;
 
+	u64 uverbs_cmd_mask;
+	u64 uverbs_ex_cmd_mask;
+
 	struct idr		idr;
 	/* spinlock protects write access to idr */
 	spinlock_t		idr_lock;

drivers/infiniband/core/uverbs_main.c

@@ -646,13 +646,13 @@ struct file *ib_uverbs_alloc_async_event_file(struct ib_uverbs_file *uverbs_file
 	return filp;
 }
 
-static bool verify_command_mask(struct ib_device *ib_dev,
-				u32 command, bool extended)
+static bool verify_command_mask(struct ib_uverbs_file *ufile, u32 command,
+				bool extended)
 {
 	if (!extended)
-		return ib_dev->uverbs_cmd_mask & BIT_ULL(command);
+		return ufile->uverbs_cmd_mask & BIT_ULL(command);
 
-	return ib_dev->uverbs_ex_cmd_mask & BIT_ULL(command);
+	return ufile->uverbs_ex_cmd_mask & BIT_ULL(command);
 }
 
 static bool verify_command_idx(u32 command, bool extended)
@@ -722,7 +722,6 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 {
 	struct ib_uverbs_file *file = filp->private_data;
 	struct ib_uverbs_ex_cmd_hdr ex_hdr;
-	struct ib_device *ib_dev;
 	struct ib_uverbs_cmd_hdr hdr;
 	bool extended;
 	int srcu_key;
@@ -757,14 +756,8 @@ static ssize_t ib_uverbs_write(struct file *filp, const char __user *buf,
 		return ret;
 
 	srcu_key = srcu_read_lock(&file->device->disassociate_srcu);
-	ib_dev = srcu_dereference(file->device->ib_dev,
-				  &file->device->disassociate_srcu);
-	if (!ib_dev) {
-		ret = -EIO;
-		goto out;
-	}
 
-	if (!verify_command_mask(ib_dev, command, extended)) {
+	if (!verify_command_mask(file, command, extended)) {
 		ret = -EOPNOTSUPP;
 		goto out;
 	}
@@ -889,6 +882,9 @@ static int ib_uverbs_open(struct inode *inode, struct file *filp)
 	mutex_unlock(&dev->lists_mutex);
 	srcu_read_unlock(&dev->disassociate_srcu, srcu_key);
 
+	file->uverbs_cmd_mask = ib_dev->uverbs_cmd_mask;
+	file->uverbs_ex_cmd_mask = ib_dev->uverbs_ex_cmd_mask;
+
 	return nonseekable_open(inode, filp);
 
 err_module: