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Subject[PATCH 3.16.y-ckt 064/126] mm: slab: only move management objects off-slab for sizes larger than KMALLOC_MIN_SIZE
3.16.7-ckt21 -stable review patch.  If anyone has any objections, please let me know.


From: Catalin Marinas <>

commit d4322d88f5fdf92729dd40f923013414fbb2184d upstream.

On systems with a KMALLOC_MIN_SIZE of 128 (arm64, some mips and powerpc
configurations defining ARCH_DMA_MINALIGN to 128), the first
kmalloc_caches[] entry to be initialised after slab_early_init = 0 is
"kmalloc-128" with index 7. Depending on the debug kernel configuration,
sizeof(struct kmem_cache) can be larger than 128 resulting in an

Commit 8fc9cf420b36 ("slab: make more slab management structure off the
slab") enables off-slab management objects for sizes starting with
PAGE_SIZE >> 5 (128 bytes for a 4KB page configuration) and the creation
of the "kmalloc-128" cache would try to place the management objects
off-slab. However, since KMALLOC_MIN_SIZE is already 128 and
freelist_size == 32 in __kmem_cache_create(), kmalloc_slab(freelist_size)
returns NULL (kmalloc_caches[7] not populated yet). This triggers the
following bug on arm64:

kernel BUG at /work/Linux/linux-2.6-aarch64/mm/slab.c:2283!
Internal error: Oops - BUG: 0 [#1] SMP
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 4.3.0-rc4+ #540
Hardware name: Juno (DT)
PC is at __kmem_cache_create+0x21c/0x280
LR is at __kmem_cache_create+0x210/0x280
Call trace:

This patch introduces an OFF_SLAB_MIN_SIZE definition to avoid off-slab
management objects for sizes equal to or smaller than KMALLOC_MIN_SIZE.

Fixes: 8fc9cf420b36 ("slab: make more slab management structure off the slab")
Signed-off-by: Catalin Marinas <>
Reported-by: Geert Uytterhoeven <>
Acked-by: Christoph Lameter <>
Cc: Pekka Enberg <>
Cc: David Rientjes <>
Cc: Joonsoo Kim <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Luis Henriques <>
mm/slab.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 9a8dc5470e5e..084985404fec 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -279,6 +279,7 @@ static void kmem_cache_node_init(struct kmem_cache_node *parent)

#define CFLGS_OFF_SLAB (0x80000000UL)
#define OFF_SLAB(x) ((x)->flags & CFLGS_OFF_SLAB)
+#define OFF_SLAB_MIN_SIZE (max_t(size_t, PAGE_SIZE >> 5, KMALLOC_MIN_SIZE + 1))

@@ -2328,7 +2329,7 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
* it too early on. Always use on-slab management when
* SLAB_NOLEAKTRACE to avoid recursive calls into kmemleak)
- if ((size >= (PAGE_SIZE >> 5)) && !slab_early_init &&
+ if (size >= OFF_SLAB_MIN_SIZE && !slab_early_init &&
* Size is large, assume best to place the slab management obj
@@ -2392,7 +2393,7 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
* This is a possibility for one of the kmalloc_{dma,}_caches.
* But since we go off slab only for object size greater than
- * PAGE_SIZE/8, and kmalloc_{dma,}_caches get created
+ * OFF_SLAB_MIN_SIZE, and kmalloc_{dma,}_caches get created
* in ascending order,this should not happen at all.
* But leave a BUG_ON for some lucky dude.

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