Re: VFS: Busy inodes after unmount on 2 way SMP

["H. Peter Anvin" <hpa@zytor.com>]

Arun Sharma wrote:
> 
> We've seen a few "VFS: Busy inodes after unmount. Self-destruct in 5
> seconds.  Have a nice day.." messages on a dual processor NFS client.
> Here's the use case:
> 
> - Due to network load issues, the NFS server becomes unreachable for
> some time
> - The automounter tries to expire the mount
> - The unmount finds a couple of busy inodes. Putting some debug printks
> shows that typically two inodes are busy i.e. have inode->i_count == 1.
> But they don't have any waiters on inode->i_wait. Further, the inodes
> that are busy are
> /mnt/foo     -> autofs mount point
> /mnt/foo/bar -> bar is a symbolic link
> 
> It's not clear if this is a NFS issue or a autofs issue, but it's seen
> often with autofs. Are there any known race conditions that have been
> fixed after 2.4.20 ? The two calls I'm worried about are:
> 
> fs/autofs/root.c:305:    d_instantiate(dentry, iget(dir->i_sb,ent->ino));
> fs/autofs/root.c:416:    d_instantiate(dentry, iget(dir->i_sb,ino));
> 

Which version of autofs are you running?  What version of mount(8)?

It's possible NFS lets you umount a mount which has busy inodes under
certain conditions.  autofs stresses mounting/umounting NFS in ways that
sometimes exposes bugs that otherwise wouldn't be seen.

	-hpa