linux-kernel - Re: Race between generic_forget_inode() and sync_sb

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Date:	Fri, 30 Nov 2007 10:03:47 +1100
From:	Neil Brown <neilb@...e.de>
To:	David Chinner <dgc@....com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: Race between generic_forget_inode() and sync_sb_inodes()?

On Friday November 30, dgc@....com wrote:
> On Fri, Nov 30, 2007 at 09:07:06AM +1100, Neil Brown wrote:
> > 
> > Hi David,
> > 
> > On Friday November 30, dgc@....com wrote:
> > > 
> > > 
> > > I came across this because I've been making changes to XFS to avoid the
> > > inode hash, and I've found that I need to remove the inode from the
> > > dirty list when setting I_WILL_FREE to avoid this race. I can't see
> > > how this race is avoided when inodes are hashed, so I'm wondering
> > > if we've just been lucky or there's something that I'm missing that
> > > means the above does not occur.
> > 
> > Looking at inode.c in 2.6.23-mm1, in generic_forget_inode, I see code:
> > 
> > 	if (!hlist_unhashed(&inode->i_hash)) {
> > 		if (!(inode->i_state & (I_DIRTY|I_SYNC)))
> > 			list_move(&inode->i_list, &inode_unused);
> > 
> > so it looks to me like:
> >    If the inode is hashed and dirty, then move it (off the s_dirty
> >    list) to inode_unused.
> 
> That check is for if the inode is _not_ dirty or being sync, right?
> Or have I just not had enough coffee this morning?

:-)  And I cannot even blame the lack of coffee as I don't drink it.

My second guess is that we have been lucky.... which is hard to believe.

I wonder if iput (and even iget) should BUG on I_WILL_FREE as well...

Perplexed.

NeilBrown
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