linux-kernel - Re: [PATCH] memory hotplug: fix early allocation handling

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Message-ID: <20080520144850.GO4146@shadowen.org>
Date:	Tue, 20 May 2008 15:48:51 +0100
From:	Andy Whitcroft <apw@...dowen.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <haveblue@...ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasunori Goto <y-goto@...fujitsu.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memory hotplug: fix early allocation handling

On Tue, May 20, 2008 at 12:51:45PM +0200, Heiko Carstens wrote:
> From: Heiko Carstens <heiko.carstens@...ibm.com>
> 
> Trying to add memory via add_memory() from within an initcall function
> results in
> 
> bootmem alloc of 163840 bytes failed!
> Kernel panic - not syncing: Out of memory
> 
> This is caused by zone_wait_table_init() which uses system_state to
> decide if it should use the bootmem allocator or not.
> When initcalls are handled the system_state is still SYSTEM_BOOTING
> but the bootmem allocator doesn't work anymore. So the allocation
> will fail.
> 
> To fix this use slab_is_available() instead as indicator like we do
> it everywhere else.
> 
> Cc: Andy Whitcroft <apw@...dowen.org>
> Cc: Dave Hansen <haveblue@...ibm.com>
> Cc: Gerald Schaefer <gerald.schaefer@...ibm.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Yasunori Goto <y-goto@...fujitsu.com>
> Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
> ---
>  mm/page_alloc.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/mm/page_alloc.c
> ===================================================================
> --- linux-2.6.orig/mm/page_alloc.c
> +++ linux-2.6/mm/page_alloc.c
> @@ -2804,7 +2804,7 @@ int zone_wait_table_init(struct zone *zo
>  	alloc_size = zone->wait_table_hash_nr_entries
>  					* sizeof(wait_queue_head_t);
>  
> - 	if (system_state == SYSTEM_BOOTING) {
> + 	if (!slab_is_available()) {
>  		zone->wait_table = (wait_queue_head_t *)
>  			alloc_bootmem_node(pgdat, alloc_size);
>  	} else {

It would be nice to be able to check that bootmem is enabled separatly
from whether slab is available, as I am sure there is a time where
neither is available during the change over.  But the change looks
reasonable as we cannot use vmalloc until slab is working.

Reviewed-by: Andy Whitcroft <apw@...dowen.org>

-apw
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