[PATCH] eventfs: Initialise ei->children before it can be freed

[PATCH] eventfs: Initialise ei->children before it can be freed

[David Carlier]

eventfs_create_events_dir() runs INIT_LIST_HEAD(&ei->children) only after
tracefs_get_inode() succeeds, but that call's failure path jumps to "fail",
which calls cleanup_ei() and then free_ei(). free_ei() reads the list with
WARN_ON_ONCE(!list_empty(&ei->children)), and alloc_root_ei() uses
kzalloc(), so children.next is NULL there and the WARN fires.

The path is reachable at runtime: mkdir /sys/kernel/tracing/instances/foo
ends up in create_event_toplevel_files() and eventfs_create_events_dir().

Move both INIT_LIST_HEAD() calls up to right after the allocation.

Fixes: f0ece16ffca7 ("eventfs: Use children field for rcu head and add memory barriers")
Signed-off-by: David Carlier <devnexen@gmail.com>
---
 fs/tracefs/event_inode.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 604ba3e841d2..1d9edc99ff3f 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -779,6 +779,9 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
 	if (!ei)
 		goto fail;
 
+	INIT_LIST_HEAD(&ei->children);
+	INIT_LIST_HEAD(&ei->list);
+
 	inode = tracefs_get_inode(dentry->d_sb);
 	if (unlikely(!inode))
 		goto fail;
@@ -802,9 +805,6 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
 	ei->attr.uid = uid;
 	ei->attr.gid = gid;
 
-	INIT_LIST_HEAD(&ei->children);
-	INIT_LIST_HEAD(&ei->list);
-
 	ti = get_tracefs(inode);
 	ti->flags |= TRACEFS_EVENT_INODE;
 	ti->private = ei;
-- 
2.55.0

Re: [PATCH] eventfs: Initialise ei->children before it can be freed

[Steven Rostedt]

On Tue, 25 Aug 2026 22:57:18 +0100
David Carlier <devnexen@gmail.com> wrote:

> eventfs_create_events_dir() runs INIT_LIST_HEAD(&ei->children) only after
> tracefs_get_inode() succeeds, but that call's failure path jumps to "fail",
> which calls cleanup_ei() and then free_ei(). free_ei() reads the list with
> WARN_ON_ONCE(!list_empty(&ei->children)), and alloc_root_ei() uses
> kzalloc(), so children.next is NULL there and the WARN fires.
> 
> The path is reachable at runtime: mkdir /sys/kernel/tracing/instances/foo
> ends up in create_event_toplevel_files() and eventfs_create_events_dir().
> 
> Move both INIT_LIST_HEAD() calls up to right after the allocation.
> 
> Fixes: f0ece16ffca7 ("eventfs: Use children field for rcu head and add memory barriers")
> Signed-off-by: David Carlier <devnexen@gmail.com>

Already queued by someone else.

https://patch.msgid.link/20260824144653.54044-1-kartikey406@gmail.com

-- Steve

Re: [PATCH] eventfs: Initialise ei->children before it can be freed

[David CARLIER]

ah forgot to check, fair :)

Cheers.

On Tue, 25 Aug 2026 at 23:28, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Tue, 25 Aug 2026 22:57:18 +0100
> David Carlier <devnexen@gmail.com> wrote:
>
> > eventfs_create_events_dir() runs INIT_LIST_HEAD(&ei->children) only after
> > tracefs_get_inode() succeeds, but that call's failure path jumps to "fail",
> > which calls cleanup_ei() and then free_ei(). free_ei() reads the list with
> > WARN_ON_ONCE(!list_empty(&ei->children)), and alloc_root_ei() uses
> > kzalloc(), so children.next is NULL there and the WARN fires.
> >
> > The path is reachable at runtime: mkdir /sys/kernel/tracing/instances/foo
> > ends up in create_event_toplevel_files() and eventfs_create_events_dir().
> >
> > Move both INIT_LIST_HEAD() calls up to right after the allocation.
> >
> > Fixes: f0ece16ffca7 ("eventfs: Use children field for rcu head and add memory barriers")
> > Signed-off-by: David Carlier <devnexen@gmail.com>
>
> Already queued by someone else.
>
> https://patch.msgid.link/20260824144653.54044-1-kartikey406@gmail.com
>
> -- Steve