Re: [PATCH v3 05/21] slab: add sheaves to most caches

[Breno Leitao <leitao@debian.org>]

Hello Vlastimil,

On Fri, Jan 16, 2026 at 03:40:25PM +0100, Vlastimil Babka wrote:
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -7863,6 +7863,48 @@ static void set_cpu_partial(struct kmem_cache *s)
>  #endif
>  }
>  
> +static unsigned int calculate_sheaf_capacity(struct kmem_cache *s,
> +					     struct kmem_cache_args *args)
> +
> +{
> +	unsigned int capacity;
> +	size_t size;
> +
> +
> +	if (IS_ENABLED(CONFIG_SLUB_TINY) || s->flags & SLAB_DEBUG_FLAGS)
> +		return 0;
> +
> +	/* bootstrap caches can't have sheaves for now */
> +	if (s->flags & SLAB_NO_OBJ_EXT)
> +		return 0;

I've been testing this on my arm64 environment with some debug patches,
and the machine became unbootable.

I am wondering if you should avoid SLAB_NOLEAKTRACE as well. I got the
impression it is hitting this infinite loop:

        -> slab allocation
          -> kmemleak_alloc()
            -> kmem_cache_alloc(object_cache)
              -> alloc_from_pcs() / __pcs_replace_empty_main()
                -> alloc_full_sheaf() -> kzalloc()
                  -> kmemleak_alloc()
                    -> ... (infinite recursion)


What about something as:

diff --git a/mm/slub.c b/mm/slub.c
index 26804859821a..0a6481aaa744 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -7445,8 +7445,13 @@ static unsigned int calculate_sheaf_capacity(struct kmem_cache *s,
        if (IS_ENABLED(CONFIG_SLUB_TINY) || s->flags & SLAB_DEBUG_FLAGS)
                return 0;

-       /* bootstrap caches can't have sheaves for now */
-       if (s->flags & SLAB_NO_OBJ_EXT)
+       /*
+        * bootstrap caches can't have sheaves for now (SLAB_NO_OBJ_EXT).
+        * SLAB_NOLEAKTRACE caches (e.g., kmemleak's object_cache) must not
+        * have sheaves to avoid recursion when sheaf allocation triggers
+        * kmemleak tracking.
+        */
+       if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE))
                return 0;