Commit e0a42726 authored Jun 23, 2006 by Ingo Molnar Committed by Linus Torvalds Jun 23, 2006

[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>

parent 668e0d8f

mm/slab.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -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)
		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, size_t size, size_t align,
		#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).

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