Re: [git pull] vfs and fs fixes

From: Linus Torvalds
Date: Tue Apr 17 2012 - 11:02:11 EST

On Mon, Apr 16, 2012 at 10:25 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>        A bunch of endianness fixes plus a patch from bfields untangling
> dependencies between vfs and nfsd trees; in principle, we could keep it
> in nfsd tree (along with a bunch of followups that definitely belong there),
> but Miklos' stuff in fs/namei.c steps fairly close to it and overlayfs
> and unionfs series - even closer, so that would create serious PITA for
> both, whichever tree it would sit in.

Why is that double mutex taking in vfs_rename_other() safe from ABBA?

We aren't guaranteed to hold the s_vfs_rename_mutex, since the parent
directories may be the same.

And yes, we hold the i_mutex on that shared parent, but the inodes may
exist (hardlinked) in another directory, so another rename could be
doing the i_mutex in the reverse order.

Maybe there is some reason why that double lock is safe, but I don't
see it, and I want it clearly documented. So I'm not pulling this.

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