linux-kernel - Re: [syzbot] [fuse?] WARNING: refcount bug in process_scheduled

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Message-ID: <20250730020318.3428-1-hdanton@sina.com>
Date: Wed, 30 Jul 2025 10:03:17 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+9921e319bd6168140b40@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fuse?] WARNING: refcount bug in process_scheduled_works

> Date: Tue, 29 Jul 2025 14:58:32 -0700	[thread overview]
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    ced1b9e0392d Merge tag 'ata-6.17-rc1' of git://git.kernel...
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=15c89782580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d51af648924b64c9
> dashboard link: https://syzkaller.appspot.com/bug?extid=9921e319bd6168140b40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=177f7034580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=165e44a2580000

#syz test

--- x/drivers/md/md.c
+++ y/drivers/md/md.c
@@ -632,10 +632,13 @@ static void mddev_delayed_delete(struct
 
 static void __mddev_put(struct mddev *mddev)
 {
+	struct kobject *kobj = &mddev->kobj;
+
 	if (mddev->raid_disks || !list_empty(&mddev->disks) ||
 	    mddev->ctime || mddev->hold_active)
 		return;
 
+	BUG_ON(kref_read(&kobj->kref) < 1);
 	/*
 	 * Call queue_work inside the spinlock so that flush_workqueue() after
 	 * mddev_find will succeed in waiting for the work to be done.
@@ -710,6 +713,7 @@ int mddev_init(struct mddev *mddev)
 
 	INIT_WORK(&mddev->sync_work, md_start_sync);
 	INIT_WORK(&mddev->del_work, mddev_delayed_delete);
+	kobject_init(&mddev->kobj, &md_ktype);
 
 	return 0;
 }
@@ -5982,7 +5986,6 @@ struct mddev *md_alloc(dev_t dev, char *
 	if (error)
 		goto out_put_disk;
 
-	kobject_init(&mddev->kobj, &md_ktype);
 	error = kobject_add(&mddev->kobj, &disk_to_dev(disk)->kobj, "%s", "md");
 	if (error) {
 		/*
--