[PATCH v2] eventfs: Add WARN_ON_ONCE() to checks in eventfs_root_lookup()

[Steven Rostedt]

}From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>

There's a couple of if statements in eventfs_root_lookup() that should
never be true. Instead of removing them, add WARN_ON_ONCE() around them.

  One is a tracefs_inode not being for eventfs.

  The other is a child being freed but still on the parent's children
  list. When a child is freed, it is removed from the list under the
  same mutex that is held during the iteration.

Link: https://lore.kernel.org/linux-trace-kernel/20240201002719.GS2087318@ZenIV/

Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
Changes since v1: https://lore.kernel.org/linux-trace-kernel/20240201161617.499712009@xxxxxxxxxxx

- Fixed missing open parenthesis in first WARN_ON_ONCE()

 fs/tracefs/event_inode.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 110e8a272189..9d9c7dc3114b 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -483,7 +483,7 @@ static struct dentry *eventfs_root_lookup(struct inode *dir,
 	struct dentry *result = NULL;
 
 	ti = get_tracefs(dir);
-	if (!(ti->flags & TRACEFS_EVENT_INODE))
+	if (WARN_ON_ONCE(!(ti->flags & TRACEFS_EVENT_INODE)))
 		return ERR_PTR(-EIO);
 
 	mutex_lock(&eventfs_mutex);
@@ -495,7 +495,8 @@ static struct dentry *eventfs_root_lookup(struct inode *dir,
 	list_for_each_entry(ei_child, &ei->children, list) {
 		if (strcmp(ei_child->name, name) != 0)
 			continue;
-		if (ei_child->is_freed)
+		/* A child is freed and removed from the list at the same time */
+		if (WARN_ON_ONCE(ei_child->is_freed))
 			goto out;
 		result = lookup_dir_entry(dentry, ei, ei_child);
 		goto out;
-- 
2.43.0