This is a note to let you know that I've just added the patch titled
mm/slab: fix unexpected index mapping result of kmalloc_size(INDEX_NODE+1)
to the 4.2-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-fix-unexpected-index-mapping-result-of-kmalloc_size-index_node-1.patch
and it can be found in the queue-4.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 03a2d2a3eafe4015412cf4e9675ca0e2d9204074 Mon Sep 17 00:00:00 2001
From: Joonsoo Kim <js1304@xxxxxxxxx>
Date: Thu, 1 Oct 2015 15:36:54 -0700
Subject: mm/slab: fix unexpected index mapping result of kmalloc_size(INDEX_NODE+1)
From: Joonsoo Kim <js1304@xxxxxxxxx>
commit 03a2d2a3eafe4015412cf4e9675ca0e2d9204074 upstream.
Commit description is copied from the original post of this bug:
http://comments.gmane.org/gmane.linux.kernel.mm/135349
Kernels after v3.9 use kmalloc_size(INDEX_NODE + 1) to get the next
larger cache size than the size index INDEX_NODE mapping. In kernels
3.9 and earlier we used malloc_sizes[INDEX_L3 + 1].cs_size.
However, sometimes we can't get the right output we expected via
kmalloc_size(INDEX_NODE + 1), causing a BUG().
The mapping table in the latest kernel is like:
index = {0, 1, 2 , 3, 4, 5, 6, n}
size = {0, 96, 192, 8, 16, 32, 64, 2^n}
The mapping table before 3.10 is like this:
index = {0 , 1 , 2, 3, 4 , 5 , 6, n}
size = {32, 64, 96, 128, 192, 256, 512, 2^(n+3)}
The problem on my mips64 machine is as follows:
(1) When configured DEBUG_SLAB && DEBUG_PAGEALLOC && DEBUG_LOCK_ALLOC
&& DEBUG_SPINLOCK, the sizeof(struct kmem_cache_node) will be "150",
and the macro INDEX_NODE turns out to be "2": #define INDEX_NODE
kmalloc_index(sizeof(struct kmem_cache_node))
(2) Then the result of kmalloc_size(INDEX_NODE + 1) is 8.
(3) Then "if(size >= kmalloc_size(INDEX_NODE + 1)" will lead to "size
= PAGE_SIZE".
(4) Then "if ((size >= (PAGE_SIZE >> 3))" test will be satisfied and
"flags |= CFLGS_OFF_SLAB" will be covered.
(5) if (flags & CFLGS_OFF_SLAB)" test will be satisfied and will go to
"cachep->slabp_cache = kmalloc_slab(slab_size, 0u)", and the result
here may be NULL while kernel bootup.
(6) Finally,"BUG_ON(ZERO_OR_NULL_PTR(cachep->slabp_cache));" causes the
BUG info as the following shows (may be only mips64 has this problem):
This patch fixes the problem of kmalloc_size(INDEX_NODE + 1) and removes
the BUG by adding 'size >= 256' check to guarantee that all necessary
small sized slabs are initialized regardless sequence of slab size in
mapping table.
Fixes: e33660165c90 ("slab: Use common kmalloc_index/kmalloc_size...")
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Reported-by: Liuhailong <liu.hailong6@xxxxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/slab.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2190,9 +2190,16 @@ __kmem_cache_create (struct kmem_cache *
size += BYTES_PER_WORD;
}
#if FORCED_DEBUG && defined(CONFIG_DEBUG_PAGEALLOC)
- if (size >= kmalloc_size(INDEX_NODE + 1)
- && cachep->object_size > cache_line_size()
- && ALIGN(size, cachep->align) < PAGE_SIZE) {
+ /*
+ * To activate debug pagealloc, off-slab management is necessary
+ * requirement. In early phase of initialization, small sized slab
+ * doesn't get initialized so it would not be possible. So, we need
+ * to check size >= 256. It guarantees that all necessary small
+ * sized slab is initialized in current slab initialization sequence.
+ */
+ if (!slab_early_init && size >= kmalloc_size(INDEX_NODE) &&
+ size >= 256 && cachep->object_size > cache_line_size() &&
+ ALIGN(size, cachep->align) < PAGE_SIZE) {
cachep->obj_offset += PAGE_SIZE - ALIGN(size, cachep->align);
size = PAGE_SIZE;
}
Patches currently in stable-queue which might be from js1304@xxxxxxxxx are
queue-4.2/mm-slab-fix-unexpected-index-mapping-result-of-kmalloc_size-index_node-1.patch
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