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SubjectRe: [PATCH] Re: Sparc32: random invalid instruction occourances on sparc32 (sun4c)
Hi David,

I tried the previous patch and it looks like it fixes the issue however
one of the test builds I did caused depmod to use up all available memory
(40M - kernel memory) before taking out the kernel with the oom killer.
At present, I do not know if it is a depmod issue or a kernel issue.
I will have to do some more tests later on to day.

I have looked at the latest patch below and am I am still not sure about
two areas. Please take a look at my offering based on your latest
patch (included here to it will probably get mangled).

Note the change to lines 2178 to 2185. I have also changed/moved the
alignment of size (see lines 2197 to 2206) based on your changes.

--- linux-2.6/mm/slab.c 2007-07-03 19:09:48.000000000 +0100
+++ linux-test/mm/slab.c 2007-07-04 04:14:15.000000000 +0100
@@ -137,6 +137,7 @@

/* Shouldn't this be in a header file somewhere? */
#define BYTES_PER_WORD sizeof(void *)
+#define RED_ZONE_ALIGN_MASK (max(__alignof__(void *), __alignof(unsigned long long)) - 1)

#ifndef cache_line_size
#define cache_line_size() L1_CACHE_BYTES
@@ -547,7 +548,7 @@ static unsigned long long *dbg_redzone2(
if (cachep->flags & SLAB_STORE_USER)
return (unsigned long long *)(objp + cachep->buffer_size -
sizeof(unsigned long long) -
- BYTES_PER_WORD);
+ max(BYTES_PER_WORD, __alignof__(unsigned long long)));
return (unsigned long long *) (objp + cachep->buffer_size -
sizeof(unsigned long long));
}
@@ -2178,7 +2179,8 @@ kmem_cache_create (const char *name, siz
* above the next power of two: caches with object sizes just above a
* power of two have a significant amount of internal fragmentation.
*/
- if (size < 4096 || fls(size - 1) == fls(size-1 + 3 * BYTES_PER_WORD))
+ if (size < 4096 || fls(size - 1) == fls(size-1 + 2 * sizeof(unsigned long long) +
+ max(BYTES_PER_WORD, __alignof__(unsigned long long))))
flags |= SLAB_RED_ZONE | SLAB_STORE_USER;
if (!(flags & SLAB_DESTROY_BY_RCU))
flags |= SLAB_POISON;
@@ -2197,9 +2199,9 @@ kmem_cache_create (const char *name, siz
* unaligned accesses for some archs when redzoning is used, and makes
* sure any on-slab bufctl's are also correctly aligned.
*/
- if (size & (BYTES_PER_WORD - 1)) {
- size += (BYTES_PER_WORD - 1);
- size &= ~(BYTES_PER_WORD - 1);
+ if (size & RED_ZONE_ALIGN_MASK) {
+ size += RED_ZONE_ALIGN_MASK;
+ size &= ~RED_ZONE_ALIGN_MASK;
}

/* calculate the final buffer alignment: */
@@ -2261,9 +2263,14 @@ kmem_cache_create (const char *name, siz
}
if (flags & SLAB_STORE_USER) {
/* user store requires one word storage behind the end of
- * the real object.
+ * the real object. But if the second red zone must be
+ * aligned 'better' than that, allow for it.
*/
- size += BYTES_PER_WORD;
+ if (flags & SLAB_RED_ZONE
+ && BYTES_PER_WORD < __alignof__(unsigned long long))
+ size += __alignof__(unsigned long long);
+ else
+ size += BYTES_PER_WORD;
}
#if FORCED_DEBUG && defined(CONFIG_DEBUG_PAGEALLOC)
if (size >= malloc_sizes[INDEX_L3 + 1].cs_size
---
Let me know if you would like an un-mangled copy of the patch as an
attachement.

Regards
Mark Fortescue.

On Tue, 3 Jul 2007, David Woodhouse wrote:

> On Tue, 2007-07-03 at 23:47 +0100, Mark Fortescue wrote:
>> Hi David,
>>
>> I will try out your patch shortly.
>
> Thanks.
>
>> I may be wrong about the size calculations but if you take a look at lines
>> 2174 to 2188 and 2207 to 2203, reading the comments suggest to me that
>> these need to be changed to match the changes to the RedZone words.
>> Failing to change these means that 32bit aligned access of the 64bit
>> RedZone words is still posible and this will kill sun4c.
>
> Why do we need more than the existing:
>
> if (flags & SLAB_RED_ZONE || flags & SLAB_STORE_USER)
> ralign = __alignof__(unsigned long long);
>
>> For the 64bit RedZone word to be 64bit aligned (required by sun4c), the
>> User word must be 64bit aligned. I don't see where in your patch, this is
>> enforced.
>
> Where __alignof__(long long) > BYTES_PER_WORD my patch should lead to
> this layout (32-bit words):
>
> [ redzone1 bits 63-32 ]
> [ redzone1 bits 31-0 ]
> [ ... object ... ]
> [ ... object ... ]
> [ redzone2 bits 63-32 ]
> [ redzone2 bits 31-0 ]
> [ unused ]
> [ user word ]
>
> The user word is a 32-bit value; there's no requirement for _it_ to be
> aligned.
>
> Hm, actually I think my patch may be incomplete -- I need to adjust the
> size of the actual object too. This patch should be better...
>
> diff --git a/mm/slab.c b/mm/slab.c
> index a9c4472..8081c07 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -547,7 +547,7 @@ static unsigned long long *dbg_redzone2(struct kmem_cache *cachep, void *objp)
> if (cachep->flags & SLAB_STORE_USER)
> return (unsigned long long *)(objp + cachep->buffer_size -
> sizeof(unsigned long long) -
> - BYTES_PER_WORD);
> + max(BYTES_PER_WORD, __alignof__(unsigned long long)));
> return (unsigned long long *) (objp + cachep->buffer_size -
> sizeof(unsigned long long));
> }
> @@ -2223,8 +2223,11 @@ kmem_cache_create (const char *name, size_t size, size_t align,
> * overridden by architecture or caller mandated alignment if either
> * is greater than BYTES_PER_WORD.
> */
> - if (flags & SLAB_RED_ZONE || flags & SLAB_STORE_USER)
> + if (flags & SLAB_RED_ZONE || flags & SLAB_STORE_USER) {
> ralign = __alignof__(unsigned long long);
> + size += (__alignof__(unsigned long long) - 1);
> + size &= ~(__alignof__(unsigned long long) - 1);
> + }
>
> /* 2) arch mandated alignment */
> if (ralign < ARCH_SLAB_MINALIGN) {
> @@ -2261,9 +2264,14 @@ kmem_cache_create (const char *name, size_t size, size_t align,
> }
> if (flags & SLAB_STORE_USER) {
> /* user store requires one word storage behind the end of
> - * the real object.
> + * the real object. But if the second red zone must be
> + * aligned 'better' than that, allow for it.
> */
> - size += BYTES_PER_WORD;
> + if (flags & SLAB_RED_ZONE
> + && BYTES_PER_WORD < __alignof__(unsigned long long))
> + size += __alignof__(unsigned long long);
> + else
> + size += BYTES_PER_WORD;
> }
> #if FORCED_DEBUG && defined(CONFIG_DEBUG_PAGEALLOC)
> if (size >= malloc_sizes[INDEX_L3 + 1].cs_size
>
>
> --
> dwmw2
>
>
-
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