linux-kernel - Re: [RFC/PATCH 2/8] revoke: inode revoke lock V7

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Date:	Wed, 19 Dec 2007 22:23:30 +0200 (EET)
From:	Pekka J Enberg <penberg@...helsinki.fi>
To:	"Serge E. Hallyn" <serue@...ibm.com>
cc:	serge@...lyn.com, alan@...hat.com, viro@...iv.linux.org.uk,
	hch@...radead.org, peterz@...radead.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC/PATCH 2/8] revoke: inode revoke lock V7

Hi,

On Wed, 19 Dec 2007, Serge E. Hallyn wrote:
> > I assume you mean S_REVOKE_LOCK and not ->i_mutex, right?
> 
> No I did mean the i_mutex since you take the i_mutex when you set
> S_REVOKE_LOCK.  So between that and the comment above do_lookup(),
> I assumed you were trying to lock out concurrent do_lookups() returning
> an inode whose revoke is starting at the same time.

No, I only use ->i_mutex for synchronizing the write to ->i_flags.

On Wed, 19 Dec 2007, Serge E. Hallyn wrote:
> > The caller is supposed to block open(2) with chmod(2)/chattr(2) so while 
> > revoke is in progress, you can get references to the _revoked inode_, 
> > which is fine (operations on it will fail with EBADFS). The 
> > ->i_revoke_wait bits are there to make sure that while we revoke, you 
> > can't get a _new reference_ to the inode until we're done.
> 
> And a new reference means through iget(), so if revoke starts
> between the IS_REVOKE_LOCKED() check in do_lookup and its return,
> it's ok bc we'll get a reference later on?

Yes, as soon as we unhash the dentries and the inode, do_lookup() will try 
to find a new inode with iget() but we need to wait before writeback on 
the revoked inode is finished.

On Wed, 19 Dec 2007, Serge E. Hallyn wrote:
> I'm a little confused but i'll keep looking.

I don't blame you. The patch is missing the following "minor detail" which 
is needed to avoid fs corruption...

			Pekka

Index: 2.6/fs/revoke.c
===================================================================
--- 2.6.orig/fs/revoke.c	2007-12-16 19:57:40.000000000 +0200
+++ 2.6/fs/revoke.c	2007-12-19 18:03:13.000000000 +0200
@@ -426,6 +426,8 @@ 	int err = 0;
 	make_revoked_inode(inode);
 	remove_inode_hash(inode);
 	revoke_aliases(inode);
+
+	err = write_inode_now(inode, 1);
 failed:
 	revoke_unlock(inode);
 	wake_up(&inode->i_revoke_wait);
--
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