Re: [PATCH 14/18] fs: Protect inode->i_state with th einode->i_lock

[Dave Chinner]

On Sat, Oct 09, 2010 at 08:52:27AM -0600, Matthew Wilcox wrote:
> On Fri, Oct 08, 2010 at 07:04:28PM +1100, Dave Chinner wrote:
> > > > @@ -884,9 +897,9 @@ struct inode *new_inode(struct super_block *sb)
> > > >  	inode = alloc_inode(sb);
> > > >  	if (inode) {
> > > >  		spin_lock(&inode_lock);
> > > > -		__inode_add_to_lists(sb, NULL, inode);
> > > >  		inode->i_ino = ++last_ino;
> > > >  		inode->i_state = 0;
> > > > +		__inode_add_to_lists(sb, NULL, inode);
> > > >  		spin_unlock(&inode_lock);
> > > >  	}
> > > >  	return inode;
> > > 
> > > What's the point in doing this move?
> > 
> > hmmmm, let me think on that....
> > 
> > > 
> > > > @@ -953,8 +966,8 @@ static struct inode *get_new_inode(struct super_block *sb,
> > > >  			if (set(inode, data))
> > > >  				goto set_failed;
> > > >  
> > > > -			__inode_add_to_lists(sb, b, inode);
> > > >  			inode->i_state = I_NEW;
> > > > +			__inode_add_to_lists(sb, b, inode);
> > > 
> > > Same here.
> > 
> > Ah, done thinking now! I was so the i_state field had been set
> > before the inode was added to various lists and potentially
> > accessable to other threads. I should probably add a comment to that
> > effect, right?
> 
> If that can happen, don't we need a wmb() between the assignment to
> i_state and the list_add too?  If so, that's a good comment :-)

No, because the locking on the lists will provide the memory
barrier.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx
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