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

[Steven Rostedt]

On Tue, 28 May 2024 07:51:30 +0300
Ilkka Naulapää <digirig...@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;
 };