Patch "mm: slab: only move management objects off-slab for sizes larger than KMALLOC_MIN_SIZE" has been added to the 4.3-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    mm: slab: only move management objects off-slab for sizes larger than KMALLOC_MIN_SIZE

to the 4.3-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-slab-only-move-management-objects-off-slab-for-sizes-larger-than-kmalloc_min_size.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d4322d88f5fdf92729dd40f923013414fbb2184d Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@arm.com>
Date: Thu, 5 Nov 2015 18:45:54 -0800
Subject: mm: slab: only move management objects off-slab for sizes larger than KMALLOC_MIN_SIZE

From: Catalin Marinas <catalin.marinas@arm.com>

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
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:

  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:
    __kmem_cache_create+0x21c/0x280
    create_boot_cache+0x48/0x80
    create_kmalloc_cache+0x50/0x88
    create_kmalloc_caches+0x4c/0xf4
    kmem_cache_init+0x100/0x118
    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@arm.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/slab.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/slab.c
+++ b/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.
 		 */


Patches currently in stable-queue which might be from catalin.marinas@arm.com are

queue-4.3/lib-hexdump.c-truncate-output-in-case-of-overflow.patch
queue-4.3/mm-slab-only-move-management-objects-off-slab-for-sizes-larger-than-kmalloc_min_size.patch