On Thu, 9 Jan 2014 15:45:37 -0800
"Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> > static void inode_free_security(struct inode *inode)
> > {
> > struct inode_security_struct *isec = inode->i_security;
> > @@ -244,8 +252,7 @@ static void inode_free_security(struct i
> > list_del_init(&isec->list);
> > spin_unlock(&sbsec->isec_lock);
> >
> > - inode->i_security = NULL;
> > - kmem_cache_free(sel_inode_cache, isec);
> > + call_rcu(&isec->rcu, inode_free_rcu);
>
> Does not clearing ->i_security mean that RCU readers can traverse
> this pointer after the invocation of call_rcu()? If so, this is
> problematic. (If something else already prevents readers from getting
> here, no problem.)
This is called when we are about to free the inode. Look at
destroy_inode(). Basically, this is the same as doing:
call_rcu(&isec->rcu, inode_free_rcu);
call_rcu(&inode->i_rcu, i_callback);
Where i_callback() does the free of the inode.
If you can access inode->i_security, after a call_rcu, then you can
also access the inode itself that has just been freed.
Yes, technically, having two separate call_rcu(), the first grace
period can end before the second, but everything to remove the inode
from sight has already been set up before that first call_rcu() is
made. That means when the first call_rcu() is executed, the inode
should already be invisible to the readers.
- Steve
>
> Thanx, Paul
>
> > }
> >
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