From: Catalin Marinas <catalin.marinas@xxxxxxx>
Subject: 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
INDEX_NODE of 8.
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:
[ 0.000000] kernel BUG at /work/Linux/linux-2.6-aarch64/mm/slab.c:2283!
[ 0.000000] Internal error: Oops - BUG: 0 [#1] SMP
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.3.0-rc4+ #540
[ 0.000000] Hardware name: Juno (DT)
[ 0.000000] task: ffffffc0006962b0 ti: ffffffc00068c000 task.ti: ffffffc00068c000
[ 0.000000] PC is at __kmem_cache_create+0x21c/0x280
[ 0.000000] LR is at __kmem_cache_create+0x210/0x280
[...]
[ 0.000000] Call trace:
[ 0.000000] [<ffffffc000154948>] __kmem_cache_create+0x21c/0x280
[ 0.000000] [<ffffffc000652da4>] create_boot_cache+0x48/0x80
[ 0.000000] [<ffffffc000652e2c>] create_kmalloc_cache+0x50/0x88
[ 0.000000] [<ffffffc000652f14>] create_kmalloc_caches+0x4c/0xf4
[ 0.000000] [<ffffffc000654a9c>] kmem_cache_init+0x100/0x118
[ 0.000000] [<ffffffc0006447d4>] start_kernel+0x214/0x33c
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 <catalin.marinas@xxxxxxx>
Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [3.15+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slab.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff -puN mm/slab.c~mm-slab-only-move-management-objects-off-slab-for-sizes-larger-than-kmalloc_min_size mm/slab.c
--- a/mm/slab.c~mm-slab-only-move-management-objects-off-slab-for-sizes-larger-than-kmalloc_min_size
+++ a/mm/slab.c
@@ -282,6 +282,7 @@ static void kmem_cache_node_init(struct
#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))
#define BATCHREFILL_LIMIT 16
/*
@@ -2212,7 +2213,7 @@ __kmem_cache_create (struct kmem_cache *
* 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 &&
!(flags & SLAB_NOLEAKTRACE))
/*
* Size is large, assume best to place the slab management obj
@@ -2276,7 +2277,7 @@ __kmem_cache_create (struct kmem_cache *
/*
* 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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