From: Christoph Lameter <clameter@sgi.com>
As reported by Paul Mundt, kobjsize() does not work properly with SLOB and SLUB

that re-use parts of struct page for their own purposes. Fix it up by using

compound_order() for compound pages that don't have PageSlab set.
Reported-by: Paul Mundt <lethal@linux-sh.org>

Cc: Christoph Lameter <clameter@sgi.com>

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

---

I kept the original object size calculation for non-compound pages in this

version. It looks like the nommu code uses kobjsize() for all sorts of

interesting things.
 mm/nommu.c |   14 +++++++++-----

 1 files changed, 9 insertions(+), 5 deletions(-)
Index: slab-2.6/mm/nommu.c

===================================================================

--- slab-2.6.orig/mm/nommu.c	2008-05-22 18:59:01.000000000 +0300

+++ slab-2.6/mm/nommu.c	2008-05-22 19:00:36.000000000 +0300

@@ -109,12 +109,22 @@

 	 * If the object we have should not have ksize performed on it,

 	 * return size of 0

 	 */

-	if (!objp || (unsigned long)objp >= memory_end || !((page = virt_to_page(objp))))

+	if (!objp)

+		return 0;

+

+	if ((unsigned long) objp >= memory_end)

+		return 0;

+

+	page = virt_to_head_page(objp);

+	if (!page)

 		return 0;
 	if (PageSlab(page))

 		return ksize(objp);
+	if (PageCompound(page))

+		return PAGE_SIZE << compound_order(page);

+

 	BUG_ON(page->index < 0);

 	BUG_ON(page->index >= MAX_ORDER);
--

Works for SLAB and SLUB.  SLOB breaks well before getting to anything these

patches affect.
Acked-by: David Howells <dhowells@redhat.com>

--

Okay, I've fixed things so that it gets things aligned properly with SLOB.

This patch doesn't work for SLOB because SLOB doesn't set PG_slab on its

pages.  This causes:
	kernel BUG at mm/nommu.c:129!
Or, as gdb sees it:
Break 00000002
Program received signal SIGABRT, Aborted.

0xc0055498 in kobjsize (objp=<value optimized out>) at mm/nommu.c:129

(gdb) list

124

125		if (PageCompound(page))

126			return PAGE_SIZE << compound_order(page);

127

128		BUG_ON(page->index < 0);

129		BUG_ON(page->index >= MAX_ORDER);

130

131		return (PAGE_SIZE << page->index);

132	}

133

(gdb) bt

#0  0xc0055498 in kobjsize (objp=<value optimized out>) at mm/nommu.c:129

#1  0xc0056408 in do_mmap_pgoff (file=0xc08f7d00, addr=3231711232, len=536128, prot=5,

    flags=3758096383, pgoff=<value optimized out>) at mm/nommu.c:1010

#2  0xc008b988 in elf_fdpic_map_file (params=0xc0849eac, file=0xc08f7d00, mm=0xc0989ee0,

    what=0xc01cc00c "executable") at mm.h:1105

#3  0xc008cb98 in load_elf_fdpic_binary (bprm=0xc0988e68, regs=<value optimized out>)

    at fs/binfmt_elf_fdpic.c:345

#4  0xc0060d90 in search_binary_handler (bprm=0xc0988e68, regs=0xc0849f90) at fs/exec.c:1215

#5  0xc0061d24 in do_execve (filename=<value optimized out>, argv=0xc01e1c38, envp=0xc01e1bb0,

    regs=0xc0849f90) at fs/exec.c:1327

#6  0xc000aab0 in sys_execve (name=<value optimized out>, argv=0xc01e1c38, envp=0xc01e1bb0)

    at arch/frv/kernel/process.c:267

#7  0xc00095e0 in __syscall_call () at arch/frv/kernel/entry.S:898

#8  0xc00095e0 in __syscall_call () at arch/frv/kernel/entry.S:898

(gdb) p/x *page

$3 = {flags = 0x40000840, _count = {counter = 0x1}, {_mapcount = {counter = 0x1cfbffff}, {

      inuse = 0x1cfb, objects = 0xffff}}, {{private = 0x0, mapping = 0x0}, slab = 0x0,

    first_page = 0x0}, {index = 0xc0980056, freelist = 0xc0980056}, lru = {next = 0xc08107b8,

    prev = 0xc01e51f0}}

(gdb) up

#1  0xc0056408 in do_mmap_pgoff (file=0xc08f7d00, addr...
[ message continues ]

Okay...  The problem with SLOB is that it can return large objects (8Kb in this

case) that aren't 8-byte aligned.  This screws up FRV as it expects to be able

to use load and store-double instructions, which fault if they don't get

8-byte (double register) alignment.
David

--

Right. SLAB/SLUB align to long long. SLOB needs to do the same.
--

I fixed it by setting ARCH_KMALLOC_MINALIGN and ARCH_SLAB_MINALIGN.
David

--

what was the change exactly ?  we were seeing alignment problems on

Blackfin and we fixed it with:

http://blackfin.uclinux.org/git/?p=readonly-mirrors/linux-kernel.git;a=c...

-mike

--

The attached patch.
David

---

[PATCH] FRV: Specify the minimum slab/kmalloc alignment
From: David Howells <dhowells@redhat.com>
Specify the minimum slab/kmalloc alignment to be 8 bytes.  This fixes a crash

when SLOB is selected as the memory allocator.  The FRV arch needs this so

that it can use the load- and store-double instructions without faulting.  By

default SLOB sets the minimum to be 4 bytes.
Signed-off-by: David Howells <dhowells@redhat.com>

---
 include/asm-frv/mem-layout.h |    7 +++++++

 1 files changed, 7 insertions(+), 0 deletions(-)
diff --git a/include/asm-frv/mem-layout.h b/include/asm-frv/mem-layout.h

index 734a1d0..2947764 100644

--- a/include/asm-frv/mem-layout.h

+++ b/include/asm-frv/mem-layout.h

@@ -31,6 +31,13 @@
 #define PAGE_MASK			(~(PAGE_SIZE-1))
+/*

+ * the slab must be aligned such that load- and store-double instructions don't

+ * fault if used

+ */

+#define	ARCH_KMALLOC_MINALIGN		8

+#define	ARCH_SLAB_MINALIGN		8

+

 /*****************************************************************************/

 /*

  * virtual memory layout from kernel's point of view

--

yeah, we were already doing that ... and the problem we had that i

referred to seems to be merged already into mainline, so you shouldnt

run into it unless you're using older kernel versions

-mike

--

You should not have to do this. This is the default alignment that also

SLOB needs to follow. We need to align structures correctly for access to

long long's.
--

are you saying that slob is broken ?  i see in mm/slob.c:

#ifndef ARCH_KMALLOC_MINALIGN

#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long)

#endif

-mike

--

It should be long long instead.
SLUB:
#ifndef ARCH_KMALLOC_MINALIGN

#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)

#endif
SLAB:
#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)
--

will you post a patch to do that (and ideally delete all of the

occurrences in asm-*/ where the minalign is defined to 8) ?

-mike

--

Thanks for testing! Where do I send these patches though? There's no entry

for no-MMU in MAINTAINERS. I guess I could just send them to Andrew...
		Pekka

--

Andrew and/or Linus.
David

--

Is ksize() happy with taking the head page instead of virt_to_page(objp)?

--

ksize() takes a pointer to an object. ksize() cannot take a the pointer to

a page struct.
--

Ah, so it does. In that case, we still need to kill off the page->index

BUG_ON() bits, while PageCompound() will take care of the compound order

bits that the page->index shifting seems to have been trying to

implement, the BUG_ON() will still trigger for PAGE_SIZE page cache

pages.

--

Yes. I have no idea what the page->index check does there. The compound

page order is not stored in the index field.
--

Would someone explain to me what this is supposed to be doing?
--