Commit e0a42726 authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
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[PATCH] mm/slab.c: fix early init assumption

The SLAB bootstrap code assumes that the first two kmalloc caches created
(the INDEX_AC and INDEX_L3 kmalloc caches) wont be off-slab.  But due to AC
and L3 structure size increase in lockdep, one of them ended up being
off-slab, and subsequently crashing with:

Unable to handle kernel NULL pointer dereference at 0000000000000000 RIP:
 [<ffffffff80267478>] kmem_cache_alloc+0x26/0x7d

The fix is to introduce a bootstrap flag and to use it to prevent off-slab
caches being created so early during bootup.

(The calculation for off-slab caches is quite complex so i didnt want to
complicate things with introducing yet another INDEX_ calculation, the flag
approach is simpler and smaller.)

Signed-off-by: default avatarIngo Molnar <>
Cc: Manfred Spraul <>
Cc: Pekka Enberg <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 668e0d8f
......@@ -331,6 +331,8 @@ static __always_inline int index_of(const size_t size)
return 0;
static int slab_early_init = 1;
#define INDEX_AC index_of(sizeof(struct arraycache_init))
#define INDEX_L3 index_of(sizeof(struct kmem_list3))
......@@ -1376,6 +1378,8 @@ void __init kmem_cache_init(void)
slab_early_init = 0;
while (sizes->cs_size != ULONG_MAX) {
* For performance, all the general caches are L1 aligned.
......@@ -2106,8 +2110,12 @@ kmem_cache_create (const char *name, size_t size, size_t align,
/* Determine if the slab management is 'on' or 'off' slab. */
if (size >= (PAGE_SIZE >> 3))
* Determine if the slab management is 'on' or 'off' slab.
* (bootstrapping cannot cope with offslab caches so don't do
* it too early on.)
if ((size >= (PAGE_SIZE >> 3)) && !slab_early_init)
* Size is large, assume best to place the slab management obj
* off-slab (should allow better packing of objs).
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