[PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[Hugh Dickins]

3.0-rc won't boot with SLUB on my PowerPC G5: kernel BUG at mm/slub.c:1950!
Bisected to 1759415e630e "slub: Remove CONFIG_CMPXCHG_LOCAL ifdeffery".

After giving myself a medal for finding the BUG on line 1950 of mm/slub.c
(it's actually the
	VM_BUG_ON((unsigned long)(&pcp1) % (2 * sizeof(pcp1)));
on line 268 of the morass that is include/linux/percpu.h)
I tried the following alignment patch and found it to work.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
 include/linux/slub_def.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 3.0-rc2/include/linux/slub_def.h	2011-05-29 18:42:37.077880848 -0700
+++ linux/include/linux/slub_def.h	2011-06-12 17:17:51.000000000 -0700
@@ -43,7 +43,7 @@ struct kmem_cache_cpu {
 #ifdef CONFIG_SLUB_STATS
 	unsigned stat[NR_SLUB_STAT_ITEMS];
 #endif
-};
+} __attribute__((aligned(2 * sizeof(long))));
 
 struct kmem_cache_node {
 	spinlock_t list_lock;	/* Protect partial list and nr_partial */

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Re: [PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[Christoph Lameter]

On Sun, 12 Jun 2011, Hugh Dickins wrote:

> 3.0-rc won't boot with SLUB on my PowerPC G5: kernel BUG at mm/slub.c:1950!
> Bisected to 1759415e630e "slub: Remove CONFIG_CMPXCHG_LOCAL ifdeffery".
>
> After giving myself a medal for finding the BUG on line 1950 of mm/slub.c
> (it's actually the
> 	VM_BUG_ON((unsigned long)(&pcp1) % (2 * sizeof(pcp1)));
> on line 268 of the morass that is include/linux/percpu.h)
> I tried the following alignment patch and found it to work.

Hmmm.. The allocpercpu in alloc_kmem_cache_cpus should take care of the
alignment. Uhh.. I see that a patch that removes the #ifdef CMPXCHG_LOCAL
was not applied? Pekka?


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Re: [PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[Pekka Enberg]

On Mon, 2011-06-13 at 12:59 -0500, Christoph Lameter wrote:
> On Sun, 12 Jun 2011, Hugh Dickins wrote:
> 
> > 3.0-rc won't boot with SLUB on my PowerPC G5: kernel BUG at mm/slub.c:1950!
> > Bisected to 1759415e630e "slub: Remove CONFIG_CMPXCHG_LOCAL ifdeffery".
> >
> > After giving myself a medal for finding the BUG on line 1950 of mm/slub.c
> > (it's actually the
> > 	VM_BUG_ON((unsigned long)(&pcp1) % (2 * sizeof(pcp1)));
> > on line 268 of the morass that is include/linux/percpu.h)
> > I tried the following alignment patch and found it to work.
> 
> Hmmm.. The allocpercpu in alloc_kmem_cache_cpus should take care of the
> alignment. Uhh.. I see that a patch that removes the #ifdef CMPXCHG_LOCAL
> was not applied? Pekka?

This patch?

http://git.kernel.org/?p=linux/kernel/git/penberg/slab-2.6.git;a=commitdiff;h=d4d84fef6d0366b585b7de13527a0faeca84d9ce

It's queued and will be sent to Linus soon.

			Pekka


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Re: [PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[Christoph Lameter]

On Mon, 13 Jun 2011, Pekka Enberg wrote:

> > Hmmm.. The allocpercpu in alloc_kmem_cache_cpus should take care of the
> > alignment. Uhh.. I see that a patch that removes the #ifdef CMPXCHG_LOCAL
> > was not applied? Pekka?
>
> This patch?
>
> http://git.kernel.org/?p=linux/kernel/git/penberg/slab-2.6.git;a=commitdiff;h=d4d84fef6d0366b585b7de13527a0faeca84d9ce
>
> It's queued and will be sent to Linus soon.

Ok it will also fix Hugh's problem then.

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Re: [PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[Pekka Enberg]

On Mon, Jun 13, 2011 at 10:29 PM, Christoph Lameter <cl@linux.com> wrote:
> On Mon, 13 Jun 2011, Pekka Enberg wrote:
>
>> > Hmmm.. The allocpercpu in alloc_kmem_cache_cpus should take care of the
>> > alignment. Uhh.. I see that a patch that removes the #ifdef CMPXCHG_LOCAL
>> > was not applied? Pekka?
>>
>> This patch?
>>
>> http://git.kernel.org/?p=linux/kernel/git/penberg/slab-2.6.git;a=commitdiff;h=d4d84fef6d0366b585b7de13527a0faeca84d9ce
>>
>> It's queued and will be sent to Linus soon.
>
> Ok it will also fix Hugh's problem then.

It's in Linus' tree now. Hugh, can you please confirm it fixes your machine too?

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Re: [PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[Hugh Dickins]

On Mon, Jun 13, 2011 at 1:34 PM, Pekka Enberg <penberg@kernel.org> wrote:
> On Mon, Jun 13, 2011 at 10:29 PM, Christoph Lameter <cl@linux.com> wrote:
>> On Mon, 13 Jun 2011, Pekka Enberg wrote:
>>
>>> > Hmmm.. The allocpercpu in alloc_kmem_cache_cpus should take care of the
>>> > alignment. Uhh.. I see that a patch that removes the #ifdef CMPXCHG_LOCAL
>>> > was not applied? Pekka?
>>>
>>> This patch?
>>>
>>> http://git.kernel.org/?p=linux/kernel/git/penberg/slab-2.6.git;a=commitdiff;h=d4d84fef6d0366b585b7de13527a0faeca84d9ce
>>>
>>> It's queued and will be sent to Linus soon.
>>
>> Ok it will also fix Hugh's problem then.
>
> It's in Linus' tree now. Hugh, can you please confirm it fixes your machine too?

I expect it to, thanks: I'll confirm tonight.

Hugh

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Re: [PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[Benjamin Herrenschmidt]

On Mon, 2011-06-13 at 14:00 -0700, Hugh Dickins wrote:
> On Mon, Jun 13, 2011 at 1:34 PM, Pekka Enberg <penberg@kernel.org> wrote:
> > On Mon, Jun 13, 2011 at 10:29 PM, Christoph Lameter <cl@linux.com> wrote:
> >> On Mon, 13 Jun 2011, Pekka Enberg wrote:
> >>
> >>> > Hmmm.. The allocpercpu in alloc_kmem_cache_cpus should take care of the
> >>> > alignment. Uhh.. I see that a patch that removes the #ifdef CMPXCHG_LOCAL
> >>> > was not applied? Pekka?
> >>>
> >>> This patch?
> >>>
> >>> http://git.kernel.org/?p=linux/kernel/git/penberg/slab-2.6.git;a=commitdiff;h=d4d84fef6d0366b585b7de13527a0faeca84d9ce
> >>>
> >>> It's queued and will be sent to Linus soon.
> >>
> >> Ok it will also fix Hugh's problem then.
> >
> > It's in Linus' tree now. Hugh, can you please confirm it fixes your machine too?
> 
> I expect it to, thanks: I'll confirm tonight.

>From report to resolution before I got to read the thread, that's how I
like them ! Thanks guys :-)

Cheers,
Ben.


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Re: [PATCH] slub: fix kernel BUG at mm/slub.c:1950!

[Hugh Dickins]

On Tue, 14 Jun 2011, Benjamin Herrenschmidt wrote:
> On Mon, 2011-06-13 at 14:00 -0700, Hugh Dickins wrote:
> > On Mon, Jun 13, 2011 at 1:34 PM, Pekka Enberg <penberg@kernel.org> wrote:
> > > On Mon, Jun 13, 2011 at 10:29 PM, Christoph Lameter <cl@linux.com> wrote:
> > >> On Mon, 13 Jun 2011, Pekka Enberg wrote:
> > >>
> > >>> > Hmmm.. The allocpercpu in alloc_kmem_cache_cpus should take care of the
> > >>> > alignment. Uhh.. I see that a patch that removes the #ifdef CMPXCHG_LOCAL
> > >>> > was not applied? Pekka?
> > >>>
> > >>> This patch?
> > >>>
> > >>> http://git.kernel.org/?p=linux/kernel/git/penberg/slab-2.6.git;a=commitdiff;h=d4d84fef6d0366b585b7de13527a0faeca84d9ce
> > >>>
> > >>> It's queued and will be sent to Linus soon.
> > >>
> > >> Ok it will also fix Hugh's problem then.
> > >
> > > It's in Linus' tree now. Hugh, can you please confirm it fixes your machine too?
> > 
> > I expect it to, thanks: I'll confirm tonight.
> 
> From report to resolution before I got to read the thread, that's how I
> like them ! Thanks guys :-)

Confirmed: fixed in 3.0-rc3 - thank you!

Hugh

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