[PATCH RFC POC 38/50] perf: stop putting the event descriptor back on failure

[Christian Brauner]

Rely on the fd exit path machinery.

Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
---
 kernel/events/core.c | 31 +++++++++++--------------------
 1 file changed, 11 insertions(+), 20 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index a6c8e38a3110..54834a7aca53 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -13924,7 +13924,7 @@ SYSCALL_DEFINE5(perf_event_open,
 	struct file *event_file = NULL;
 	struct task_struct *task = NULL;
 	struct pmu *pmu;
-	int event_fd;
+	const struct fd_slot *event_fd;
 	int move_group = 0;
 	int err;
 	int f_flags = O_RDWR;
@@ -13990,9 +13990,9 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (flags & PERF_FLAG_FD_CLOEXEC)
 		f_flags |= O_CLOEXEC;
 
-	event_fd = get_unused_fd_flags(f_flags);
-	if (event_fd < 0)
-		return event_fd;
+	event_fd = fd_prepare(f_flags);
+	if (IS_ERR(event_fd))
+		return PTR_ERR(event_fd);
 
 	/*
 	 * Event creation should be under SRCU, see perf_pmu_unregister().
@@ -14001,15 +14001,11 @@ SYSCALL_DEFINE5(perf_event_open,
 
 	CLASS(fd, group)(group_fd);     // group_fd == -1 => empty
 	if (group_fd != -1) {
-		if (!is_perf_file(group)) {
-			err = -EBADF;
-			goto err_fd;
-		}
+		if (!is_perf_file(group))
+			return -EBADF;
 		group_leader = fd_file(group)->private_data;
-		if (group_leader->state <= PERF_EVENT_STATE_EXIT) {
-			err = -ENODEV;
-			goto err_fd;
-		}
+		if (group_leader->state <= PERF_EVENT_STATE_EXIT)
+			return -ENODEV;
 		if (flags & PERF_FLAG_FD_OUTPUT)
 			output_event = group_leader;
 		if (flags & PERF_FLAG_FD_NO_GROUP)
@@ -14018,10 +14014,8 @@ SYSCALL_DEFINE5(perf_event_open,
 
 	if (pid != -1 && !(flags & PERF_FLAG_PID_CGROUP)) {
 		task = find_lively_task_by_vpid(pid);
-		if (IS_ERR(task)) {
-			err = PTR_ERR(task);
-			goto err_fd;
-		}
+		if (IS_ERR(task))
+			return PTR_ERR(task);
 	}
 
 	if (task && group_leader &&
@@ -14298,8 +14292,7 @@ SYSCALL_DEFINE5(perf_event_open,
 	 * This ensures destruction of the group leader will find
 	 * the pointer to itself in perf_group_detach().
 	 */
-	fd_install(event_fd, event_file);
-	return event_fd;
+	return fd_stage(event_fd, event_file);
 
 err_context:
 	put_pmu_ctx(event->pmu_ctx);
@@ -14316,8 +14309,6 @@ SYSCALL_DEFINE5(perf_event_open,
 err_task:
 	if (task)
 		put_task_struct(task);
-err_fd:
-	put_unused_fd(event_fd);
 	return err;
 }
 

-- 
2.53.0