Re: Bug in Kernel 6.8.x, 6.9.x Causing Trace/Panic During Shutdown/Reboot

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 28 May 2024 07:51:30 +0300
Ilkka Naulapää <digirigawa@gmail.com> wrote:

> yeah, the cache_from_obj tracing bug (without panic) has been
> displayed quite some time now - maybe even since 6.7.x or so. I could
> try checking a few versions back for this and try bisecting it if I
> can find when this started.
> 

OK, so I don't think the commit your last bisect hit is the cause of
the bug. It added a delay (via RCU) and is causing the real bug to blow
up more.

Can you add this patch to v6.9.2 and hopefully it crashes in a better
location that we can find where the mixup happened.

You may need to add the other commit (too if this doesn't trigger.

Thanks,

-- Steve

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 417c840e6403..7af3f696696d 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -50,6 +50,7 @@ static struct inode *tracefs_alloc_inode(struct super_block *sb)
 	list_add_rcu(&ti->list, &tracefs_inodes);
 	spin_unlock_irqrestore(&tracefs_inode_lock, flags);
 
+	ti->magic = 20240823;
 	return &ti->vfs_inode;
 }
 
@@ -66,6 +67,7 @@ static void tracefs_free_inode(struct inode *inode)
 	struct tracefs_inode *ti = get_tracefs(inode);
 	unsigned long flags;
 
+	BUG_ON(ti->magic != 20240823);
 	spin_lock_irqsave(&tracefs_inode_lock, flags);
 	list_del_rcu(&ti->list);
 	spin_unlock_irqrestore(&tracefs_inode_lock, flags);
@@ -271,16 +273,6 @@ static const struct inode_operations tracefs_file_inode_operations = {
 	.setattr	= tracefs_setattr,
 };
 
-struct inode *tracefs_get_inode(struct super_block *sb)
-{
-	struct inode *inode = new_inode(sb);
-	if (inode) {
-		inode->i_ino = get_next_ino();
-		simple_inode_init_ts(inode);
-	}
-	return inode;
-}
-
 struct tracefs_mount_opts {
 	kuid_t uid;
 	kgid_t gid;
@@ -448,6 +440,17 @@ static const struct super_operations tracefs_super_operations = {
 	.show_options	= tracefs_show_options,
 };
 
+struct inode *tracefs_get_inode(struct super_block *sb)
+{
+	struct inode *inode = new_inode(sb);
+	BUG_ON(sb->s_op != &tracefs_super_operations);
+	if (inode) {
+		inode->i_ino = get_next_ino();
+		simple_inode_init_ts(inode);
+	}
+	return inode;
+}
+
 /*
  * It would be cleaner if eventfs had its own dentry ops.
  *
diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index f704d8348357..dda7d2708e30 100644
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h
@@ -16,6 +16,7 @@ struct tracefs_inode {
 	};
 	/* The below gets initialized with memset_after(ti, 0, vfs_inode) */
 	struct list_head	list;
+	unsigned long		magic;
 	unsigned long           flags;
 	void                    *private;
 };