From a8f324a46fbe5473633af00039e81821be0ce51b Mon Sep 17 00:00:00 2001 From: Roman Pen Date: Tue, 9 Feb 2016 11:30:29 +0100 Subject: [PATCH] debugfs: fix inode i_nlink references for automount dentry Directory inodes should start off with i_nlink == 2 (one extra ref for "." entry). debugfs_create_automount() increases neither the i_nlink reference for current inode nor for parent inode. On attempt to remove the automount dentry, kernel complains: [ 86.288070] WARNING: CPU: 1 PID: 3616 at fs/inode.c:273 drop_nlink+0x3e/0x50() [ 86.288461] Modules linked in: debugfs_example2(O-) [ 86.288745] CPU: 1 PID: 3616 Comm: rmmod Tainted: G O 4.4.0-rc3-next-20151207+ #135 [ 86.289197] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.2-20150617_082717-anatol 04/01/2014 [ 86.289696] ffffffff81be05c9 ffff8800b9e6fda0 ffffffff81352e2c 0000000000000000 [ 86.290110] ffff8800b9e6fdd8 ffffffff81065142 ffff8801399175e8 ffff8800bb78b240 [ 86.290507] ffff8801399175e8 ffff8800b73d7898 ffff8800b73d7840 ffff8800b9e6fde8 [ 86.290933] Call Trace: [ 86.291080] [] dump_stack+0x4e/0x82 [ 86.291340] [] warn_slowpath_common+0x82/0xc0 [ 86.291640] [] warn_slowpath_null+0x1a/0x20 [ 86.291932] [] drop_nlink+0x3e/0x50 [ 86.292208] [] simple_unlink+0x4b/0x60 [ 86.292481] [] simple_rmdir+0x37/0x50 [ 86.292748] [] __debugfs_remove.part.16+0xa8/0xd0 [ 86.293082] [] debugfs_remove_recursive+0xdb/0x1c0 [ 86.293406] [] cleanup_module+0x2d/0x3b [debugfs_example2] [ 86.293762] [] SyS_delete_module+0x16b/0x220 [ 86.294077] [] entry_SYSCALL_64_fastpath+0x12/0x6a [ 86.294405] ---[ end trace c9fc53353fe14a36 ]--- [ 86.294639] ------------[ cut here ]------------ To reproduce the issue it is enough to invoke these lines: autom = debugfs_create_automount("automount", NULL, vfsmount_cb, data); BUG_ON(IS_ERR_OR_NULL(autom)); debugfs_remove(autom); The issue is fixed by increasing inode i_nlink references for current and parent inodes. Signed-off-by: Roman Pen Signed-off-by: Greg Kroah-Hartman --- fs/debugfs/inode.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c index bece948..13d65f8 100644 --- a/fs/debugfs/inode.c +++ b/fs/debugfs/inode.c @@ -461,7 +461,11 @@ struct dentry *debugfs_create_automount(const char *name, inode->i_flags |= S_AUTOMOUNT; inode->i_private = data; dentry->d_fsdata = (void *)f; + /* directory inodes start off with i_nlink == 2 (for "." entry) */ + inc_nlink(inode); d_instantiate(dentry, inode); + inc_nlink(d_inode(dentry->d_parent)); + fsnotify_mkdir(d_inode(dentry->d_parent), dentry); return end_creating(dentry); } EXPORT_SYMBOL(debugfs_create_automount); -- 2.7.4