linux-kernel - Re: [WTF] ... is going on with current->fs->{root,mnt} accesses in pohmelfs

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Message-ID: <20100211030253.GQ30031@ZenIV.linux.org.uk>
Date:	Thu, 11 Feb 2010 03:02:54 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Evgeniy Polyakov <zbr@...emap.net>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [WTF] ... is going on with current->fs->{root,mnt} accesses in
 pohmelfs

On Thu, Feb 11, 2010 at 12:29:33AM +0300, Evgeniy Polyakov wrote:
> On Wed, Feb 10, 2010 at 09:02:48PM +0000, Al Viro (viro@...IV.linux.org.uk) wrote:
> > Which would be... ?  E.g. between writepages() and rename().  What serializes
> > your write_inode_create() wrt renames?  IOW, how can the server decide that
> > data from writepages() should go to the same object regardless of the
> > rename?
> 
> rename and some other metadata operations as well as write itself
> request remote lock (if not grabbed already), acknowledge forces writeback to old path.

Um.  You do realize that d_move() happens with none of your locks held,
right?  It's done in vfs_rename_{other,dir}() and the only thing held
is s_vfs_rename_sem and i_mutex on parents.  How could your code in
writeback be able to distinguish

rename() is done
d_move() has happened, we see new pathname in dcache

from

rename() is done
d_move() has not yet happened, we see old pathname in dcache

and generate the right on-the-wire traffic in both cases?  Note that here
server has already seen rename request; as far as server and client are
concerned the rename() is over.
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