On Sat, Sep 27, 2014 at 07:31:39PM +0100, Al Viro wrote: > We can get the long name cases right, and I agree that it'll make the > things nicer, but it might take a couple of days to get right. The thing > I'm concerned about is not screwing DCACHE_RCUACCESS up. FWIW, I suspect that the right approach is to put refcount + rcu_head in front of external name and do the following: * __d_free() checks if we have an external name, gets its containing structure and does if (atomic_dec_and_test(&name->count)) kfree(name); * switch_names() in non-exchange case (I'd probably call it copy_name, not move_names, but anyway) sets DCACHE_RCUACCESS on target (source has already gotten it from __d_rehash()), increments refcount on target's name if external and, if the source old name is external, decrements its refcount and calls kfree_rcu() if it has hit zero. AFAICS, it guarantees that we'll schedule an RCU callback on name's rch_head at most once, that we won't free it while RCU callback on it is scheduled and we won't free it until a grace period has expired since the last time it had been referenced by observable dentries. Do you see any holes in that? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
