[5/6] eventfs: Add WARN_ON_ONCE() to checks in eventfs_root_lookup()

Commit Message

Steven Rostedt Feb. 1, 2024, 3:34 p.m. UTC

From: "Steven Rostedt (Google)" <[e-mail]>

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 <[e-mail]>
Signed-off-by: Steven Rostedt (Google) <[e-mail]>
---
 fs/tracefs/event_inode.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Steven Rostedt Feb. 1, 2024, 5:23 p.m. UTC | #1

On Thu, 01 Feb 2024 10:34:51 -0500
Steven Rostedt <[e-mail]> wrote:

> --- 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)))

I added this patch at the end but never tested it :-p

I then did a rebase to move it ahead of patch 6, which was tested.

Will resend this patch.

-- Steve


>  		return ERR_PTR(-EIO);
>  
>  	mutex_lock(&eventfs_mutex);

Patch

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 110e8a272189..1a831ba1042b 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;