mm/slab: add rcu_barrier() to kvfree_rcu_barrier_on_cache()

After we submit the rcu_free sheaves to call_rcu() we need to make sure
the rcu callbacks complete. kvfree_rcu_barrier() does that via
flush_all_rcu_sheaves() but kvfree_rcu_barrier_on_cache() doesn't. Fix
that.

This currently causes no issues because the caches with sheaves we have
are never destroyed. The problem flagged by kernel test robot was
reported for a patch that enables sheaves for (almost) all caches, and
occurred only with CONFIG_KASAN. Harry Yoo found the root cause [1]:

  It turns out the object freed by sheaf_flush_unused() was in KASAN
  percpu quarantine list (confirmed by dumping the list) by the time
  __kmem_cache_shutdown() returns an error.

  Quarantined objects are supposed to be flushed by kasan_cache_shutdown(),
  but things go wrong if the rcu callback (rcu_free_sheaf_nobarn()) is
  processed after kasan_cache_shutdown() finishes.

  That's why rcu_barrier() in __kmem_cache_shutdown() didn't help,
  because it's called after kasan_cache_shutdown().

  Calling rcu_barrier() in kvfree_rcu_barrier_on_cache() guarantees
  that it'll be added to the quarantine list before kasan_cache_shutdown()
  is called. So it's a valid fix!

[1] https://lore.kernel.org/all/aWd6f3jERlrB5yeF@hyeyoo/

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202601121442.c530bed3-lkp@intel.com
Fixes: 0f35040de5 ("mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction")
Cc: stable@vger.kernel.org
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Tested-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

mm/slab_common.c

@@ -2133,8 +2133,11 @@ EXPORT_SYMBOL_GPL(kvfree_rcu_barrier);
  */
 void kvfree_rcu_barrier_on_cache(struct kmem_cache *s)
 {
-	if (s->cpu_sheaves)
+	if (s->cpu_sheaves) {
 		flush_rcu_sheaves_on_cache(s);
+		rcu_barrier();
+	}
+
 	/*
 	 * TODO: Introduce a version of __kvfree_rcu_barrier() that works
 	 * on a specific slab cache.