linux-kernel - Re: v3.15-rc1 slab allocator broken on m68knommu (coldfire)

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Message-Id: <201404160847.27300.sfking@fdwdc.com>
Date:	Wed, 16 Apr 2014 08:47:27 -0700
From:	Steven King <sfking@...dc.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	linux-kernel@...r.kernel.org,
	uClinux development list <uclinux-dev@...inux.org>
Subject: Re: v3.15-rc1 slab allocator broken on m68knommu (coldfire)

On Tuesday 15 April 2014 5:19:31 pm Joonsoo Kim wrote:
> On Mon, Apr 14, 2014 at 05:45:43PM -0700, Steven King wrote:
> > git bisect suggests it starts somewhere around commit
> > f315e3fa1cf5b3317fc948708645fff889ce1e63 slab: restrict the number of
> > objects in a slab
> >
> > but its kinda hard to tell as there is some compile breakage in there as
> > well.
>
> Hello, Steven.
>
> Hmm... there is the fix on upstream v3.15-rc1 for build breakage.
> See commit 24f870d('slab: fix wrongly used macro').
> If slab allocator broken with this fix, please let me know.
>
> Thanks.


Yes, 24f870d fixes the build breakage but the allocator is still broken (board
doesn't boot).  However, I was able to track down the exact changes that seem
to break things; in 8dcc774 'slab: introduce byte sized index for the freelist of a slab'
there are the changes to get_free_obj and set_free_obj:

-static inline unsigned int get_free_obj(struct page *page, unsigned int idx)
+static inline freelist_idx_t get_free_obj(struct page *page, unsigned char idx)
 {
-	return ((unsigned int *)page->freelist)[idx];
+	return ((freelist_idx_t *)page->freelist)[idx];
 }
 
 static inline void set_free_obj(struct page *page,
-					unsigned int idx, unsigned int val)
+					unsigned char idx, freelist_idx_t val)
 {
-	((unsigned int *)(page->freelist))[idx] = val;
+	((freelist_idx_t *)(page->freelist))[idx] = val;
 }
 
if I change idx back to unsigned int, ie:

diff --git a/mm/slab.c b/mm/slab.c
index 388cb1a..d7f9f44 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2572,13 +2572,13 @@ static void *alloc_slabmgmt(struct kmem_cache *cachep,
        return freelist;
 }

-static inline freelist_idx_t get_free_obj(struct page *page, unsigned char idx)
+static inline freelist_idx_t get_free_obj(struct page *page, unsigned int idx)
 {
        return ((freelist_idx_t *)page->freelist)[idx];
 }

 static inline void set_free_obj(struct page *page,
-                                       unsigned char idx, freelist_idx_t val)
+                                       unsigned int idx, freelist_idx_t val)
 {
        ((freelist_idx_t *)(page->freelist))[idx] = val;
 }


then v3.15-rc1 will boot using the slab allocator.
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