On Fri, May 11, 2018 at 03:18:43AM +0100, Al Viro wrote:
> On Fri, May 11, 2018 at 11:32:08AM +1000, Dave Chinner wrote:
>
> > i.e. we already have code in xfs_setup_inode() that sets the xfs
> > inode ILOCK rwsem dir/non-dir lockdep class before the new inode is
> > unlocked - we could just do the i_rwsem lockdep setup there, too.
>
> ... which would suffice -
>
> if (S_ISDIR(inode->i_mode)) {
> struct file_system_type *type = inode->i_sb->s_type;
>
> /* Set new key only if filesystem hasn't already changed it */
> if (lockdep_match_class(&inode->i_rwsem, &type->i_mutex_key)) {
>
> in lockdep_annotate_inode_mutex_key() would make sure that ->i_rwsem will be
> left alone by unlock_new_inode().
Ok, If you are happy with XFs doing that, I'll put together a patch
and send it out.
> > Then, if we were to factor unlock_new_inode() as Andreas suggested,
> > we could call __unlock_new_inode() from xfs_finish_inode_setup().
>
> No need - if you set the class in xfs_setup_inode(), you are fine.
>
> Said that, hash insertion is also potentially delicate - another ext2/nfsd
> race from the same pile back in 2008 had been
> * ext2_new_inode() chooses inumber
> * open-by-fhandle guesses the inumber and hits ext2_iget(), which
> inserts a locked in-core inode into icache and proceeds to block reading
> it from disk.
> * ext2_new_inode() inserts *its* in-core inode into icache (with
> the same inumber) and sets the things up, both in-core and on disk
> * open-by-fhandle is back and sees a good live on-disk inode.
> It finishes setting the in-core one up and we'd got *TWO* in-core inodes
> with the same inumber, both hashed, both with dentries, both used by
> syscalls to do IO. Good times all around - fs corruption is fun.
>
> That was fixed by using insert_inode_locked() in ext2_new_inode(), and doing
> that before the on-disk inode would start looking good. If it came during
> ext2_iget(), it would've found an in-core inode with that inumber (locked,
> doomed to be rejected), waited for it to come unlocked, see it unhashed
> (since ext2_iget() said it was no good) and inserted its in-core inode
> into hash (after having rechecked that nobody had an in-core inode with
> the same inumber in there, that is).
>
> I'm not familiar enough with XFS icache replacment to tell if anything
> of that sort is a problem there; might be a non-issue for any number
> of reasons.
I'm pretty sure we handle those cases - amongst other things we
don't trust inode numbers in filehandles and so validation of inode
numbers in incoming filehandles is serialised against
allocating/freeing of inodes before it even gets to inode cache
lookups...
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
