[PATCH 6.18 629/752] mm/slab: add rcu_barrier() to kvfree_rcu_barrier_on_cache()

Sasha Levin
2026-02-28T17:57:23Z

From: Vlastimil Babka <vbabka@suse.cz>

[ Upstream commit b55b423e8518361124ff0a9e15df431b3682ee4f ]

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: 0f35040de593 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/slab_common.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 87bde1d8916be..0f58265ca200e 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -2134,8 +2134,11 @@ 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.
--
2.51.0