On Mon, Dec 02, 2013 at 03:19:40PM +0400, Vladimir Davydov wrote:
> Using destroy_super() in alloc_super() fail path is bad, because:
>
> * It will trigger WARN_ON(!list_empty(&s->s_mounts)) since s_mounts is
> initialized after several 'goto fail's.
So let's fix that.
> * It will call kfree_rcu() to free the super block although kfree() is
> obviously enough there.
> * The list_lru structure was initially implemented without the ability
> to destroy an uninitialized object in mind.
>
> I'm going to replace the conventional list_lru with per-memcg lru to
> implement per-memcg slab reclaim. This new structure will fail
> destruction of objects that haven't been properly initialized so let's
> inline appropriate snippets from destroy_super() to alloc_super() fail
> path instead of using the whole function there.
You're basically undoing the change made in commit 7eb5e88 ("uninline
destroy_super(), consolidate alloc_super()") which was done less
than a month ago. :/
The code as it stands works just fine - the list-lru structures in
the superblock are actually initialised (to zeros) - and so calling
list_lru_destroy() on it works just fine in that state as the
pointers that are freed are NULL. Yes, unexpected, but perfectly
valid code.
I haven't looked at the internals of the list_lru changes you've
made yet, but it surprises me that we can't handle this case
internally to list_lru_destroy().
Al, your call on inlining destroy_super() in alloc_super() again....
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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