[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: Ingo Molnar <mingo@elte.hu>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/slab.c b/mm/slab.c
index e3260db..664c3a10 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -331,6 +331,8 @@
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 @@
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 @@
#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).