Re: [PATCH RFC v2 01/20] mm/slab: add rcu_barrier() to kvfree_rcu_barrier_on_cache()

[Harry Yoo]

On Mon, Jan 12, 2026 at 04:16:55PM +0100, Vlastimil Babka wrote:
> 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.

Oops, my bad.

> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-lkp/202601121442.c530bed3-lkp@xxxxxxxxx
> Fixes: 0f35040de593 ("mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---

The fix looks good to me, but I wonder why
`if (s->sheaf_capacity) rcu_barrier();` in __kmem_cache_shutdown()
didn't prevent the bug from happening?

>  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 eed7ea556cb1..ee994ec7f251 100644
> --- a/mm/slab_common.c
> +++ b/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.
> 
> -- 
> 2.52.0
> 

-- 
Cheers,
Harry / Hyeonggon