Hey Al, On Sun, Jul 12, 2015 at 04:00:35PM +0100, Al Viro wrote: > On Wed, Jul 08, 2015 at 10:41:43AM -0500, Ben Myers wrote: > > > The bug rings a bell for me so I will stick my neck out instead of > > lurking. Don't you need to sample that link count under the filesystems > > internal lock in order to avoid an unlink/iget race? I suggest creating > > a helper to prune disconnected dentries which a filesystem could call in > > .unlink. That would avoid the risk of unintended side effects with the > > d_alloc/d_free/icache approach and have provable link count correctness. > > For one thing, this patch does *not* check for i_nlink at all. I agree that no checking of i_nlink has the advantage of brevity. Anyone who is using dentry.d_fsdata with an open_by_handle workload (if there are any) will be affected. > For another, there's no such thing as 'filesystems internal lock' for > i_nlink protection - that's handled by i_mutex... And what does > iget() have to do with any of that? i_mutex is good enough only for local filesystems. Network/clustered/distributed filesystems need to take an internal lock to provide exclusion for this .unlink with a .link on another host. That's where I'm coming from with iget(). Maybe plumbing i_op.unlink with another argument to return i_nlink is something to consider? A helper for the few filesystems that need to do this might be good enough in the near term. Thanks, Ben -- 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
