From: Ingo Molnar 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: [] 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: Ingo Molnar Cc: Manfred Spraul Cc: Pekka Enberg Signed-off-by: Andrew Morton --- mm/slab.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff -puN mm/slab.c~mm-slabc-fix-early-init-assumption mm/slab.c --- devel/mm/slab.c~mm-slabc-fix-early-init-assumption 2006-06-09 15:21:51.000000000 -0700 +++ devel-akpm/mm/slab.c 2006-06-09 15:21:51.000000000 -0700 @@ -331,6 +331,8 @@ static __always_inline int index_of(cons 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) NULL, NULL); } + 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, siz #endif #endif - /* 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). _