Commit d4322d88 authored by Catalin Marinas's avatar Catalin Marinas Committed by Linus Torvalds
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mm: slab: only move management objects off-slab for sizes larger than KMALLOC_MIN_SIZE

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 8fc9cf42 ("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: 8fc9cf42

 ("slab: make more slab management structure off the slab")
Signed-off-by: default avatarCatalin Marinas <>
Reported-by: default avatarGeert Uytterhoeven <>
Acked-by: default avatarChristoph Lameter <>
Cc: Pekka Enberg <>
Cc: David Rientjes <>
Cc: Joonsoo Kim <>
Cc: <>	[3.15+]
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 9f835703
......@@ -282,6 +282,7 @@ 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))
......@@ -2212,7 +2213,7 @@ __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
......@@ -2276,7 +2277,7 @@ __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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