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

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Date:	Fri, 30 Nov 2007 09:07:06 +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()?


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.

So it seems to me that generic_forget_inode also finds it needs to
remove the inode from the dirty list when setting I_WILL_FREE.

Maybe we are looking at different kernel versions?  Maybe I
misunderstood your problem?

NeilBrown
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