Re: [PATCH v2 1/4] mm: Check for node_online in node_present_pages

[Michael Ellerman <mpe@ellerman.id.au>]

Michael Ellerman <mpe@ellerman.id.au> writes:
> Vlastimil Babka <vbabka@suse.cz> writes:
>> On 3/18/20 11:02 AM, Michal Hocko wrote:
>>> On Wed 18-03-20 12:58:07, Srikar Dronamraju wrote:
>>>> Calling a kmalloc_node on a possible node which is not yet onlined can
>>>> lead to panic. Currently node_present_pages() doesn't verify the node is
>>>> online before accessing the pgdat for the node. However pgdat struct may
>>>> not be available resulting in a crash.
>>>> 
>>>> NIP [c0000000003d55f4] ___slab_alloc+0x1f4/0x760
>>>> LR [c0000000003d5b94] __slab_alloc+0x34/0x60
>>>> Call Trace:
>>>> [c0000008b3783960] [c0000000003d5734] ___slab_alloc+0x334/0x760 (unreliable)
>>>> [c0000008b3783a40] [c0000000003d5b94] __slab_alloc+0x34/0x60
>>>> [c0000008b3783a70] [c0000000003d6fa0] __kmalloc_node+0x110/0x490
>>>> [c0000008b3783af0] [c0000000003443d8] kvmalloc_node+0x58/0x110
>>>> [c0000008b3783b30] [c0000000003fee38] mem_cgroup_css_online+0x108/0x270
>>>> [c0000008b3783b90] [c000000000235aa8] online_css+0x48/0xd0
>>>> [c0000008b3783bc0] [c00000000023eaec] cgroup_apply_control_enable+0x2ec/0x4d0
>>>> [c0000008b3783ca0] [c000000000242318] cgroup_mkdir+0x228/0x5f0
>>>> [c0000008b3783d10] [c00000000051e170] kernfs_iop_mkdir+0x90/0xf0
>>>> [c0000008b3783d50] [c00000000043dc00] vfs_mkdir+0x110/0x230
>>>> [c0000008b3783da0] [c000000000441c90] do_mkdirat+0xb0/0x1a0
>>>> [c0000008b3783e20] [c00000000000b278] system_call+0x5c/0x68
>>>> 
>>>> Fix this by verifying the node is online before accessing the pgdat
>>>> structure. Fix the same for node_spanned_pages() too.
>>>> 
>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>> Cc: linux-mm@kvack.org
>>>> Cc: Mel Gorman <mgorman@suse.de>
>>>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>>>> Cc: Sachin Sant <sachinp@linux.vnet.ibm.com>
>>>> Cc: Michal Hocko <mhocko@kernel.org>
>>>> Cc: Christopher Lameter <cl@linux.com>
>>>> Cc: linuxppc-dev@lists.ozlabs.org
>>>> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>>>> Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
>>>> Cc: Vlastimil Babka <vbabka@suse.cz>
>>>> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>>>> Cc: Bharata B Rao <bharata@linux.ibm.com>
>>>> Cc: Nathan Lynch <nathanl@linux.ibm.com>
>>>> 
>>>> Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
>>>> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
>>>> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>>>> ---
>>>>  include/linux/mmzone.h | 6 ++++--
>>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>> 
>>>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>>>> index f3f264826423..88078a3b95e5 100644
>>>> --- a/include/linux/mmzone.h
>>>> +++ b/include/linux/mmzone.h
>>>> @@ -756,8 +756,10 @@ typedef struct pglist_data {
>>>>  	atomic_long_t		vm_stat[NR_VM_NODE_STAT_ITEMS];
>>>>  } pg_data_t;
>>>>  
>>>> -#define node_present_pages(nid)	(NODE_DATA(nid)->node_present_pages)
>>>> -#define node_spanned_pages(nid)	(NODE_DATA(nid)->node_spanned_pages)
>>>> +#define node_present_pages(nid)		\
>>>> +	(node_online(nid) ? NODE_DATA(nid)->node_present_pages : 0)
>>>> +#define node_spanned_pages(nid)		\
>>>> +	(node_online(nid) ? NODE_DATA(nid)->node_spanned_pages : 0)
>>> 
>>> I believe this is a wrong approach. We really do not want to special
>>> case all the places which require NODE_DATA. Can we please go and
>>> allocate pgdat for all possible nodes?
>>> 
>>> The current state of memory less hacks subtle bugs poping up here and
>>> there just prove that we should have done that from the very begining
>>> IMHO.
>>
>> Yes. So here's an alternative proposal for fixing the current situation in SLUB,
>> before the long-term solution of having all possible nodes provide valid pgdat
>> with zonelists:
>>
>> - fix SLUB with the hunk at the end of this mail - the point is to use NUMA_NO_NODE
>>   as fallback instead of node_to_mem_node()
>> - this removes all uses of node_to_mem_node (luckily it's just SLUB),
>>   kill it completely instead of trying to fix it up
>> - patch 1/4 is not needed with the fix
>> - perhaps many of your other patches are alss not needed 
>> - once we get the long-term solution, some of the !node_online() checks can be removed
>
> Seems like a nice solution to me :)
>
>> ----8<----
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 17dc00e33115..1d4f2d7a0080 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -1511,7 +1511,7 @@ static inline struct page *alloc_slab_page(struct kmem_cache *s,
>>  	struct page *page;
>>  	unsigned int order = oo_order(oo);
>>  
>> -	if (node == NUMA_NO_NODE)
>> +	if (node == NUMA_NO_NODE || !node_online(node))
>
> Why don't we need the node_present_pages() check here?
>
>>  		page = alloc_pages(flags, order);
>>  	else
>>  		page = __alloc_pages_node(node, flags, order);
>> @@ -1973,8 +1973,6 @@ static void *get_partial(struct kmem_cache *s, gfp_t flags, int node,
>>  
>>  	if (node == NUMA_NO_NODE)
>>  		searchnode = numa_mem_id();
>> -	else if (!node_present_pages(node))
>> -		searchnode = node_to_mem_node(node);
>>  
>>  	object = get_partial_node(s, get_node(s, searchnode), c, flags);
>>  	if (object || node != NUMA_NO_NODE)
>> @@ -2568,12 +2566,15 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>>  redo:
>>  
>>  	if (unlikely(!node_match(page, node))) {
>> -		int searchnode = node;
>> -
>> -		if (node != NUMA_NO_NODE && !node_present_pages(node))
>> -			searchnode = node_to_mem_node(node);
>> -
>> -		if (unlikely(!node_match(page, searchnode))) {
>> +		/*
>> +		 * node_match() false implies node != NUMA_NO_NODE
>> +		 * but if the node is not online and has no pages, just
>                                                  ^
>                                                  this should be 'or' ?

Sorry I see you've already fixed this in the version you posted.

cheers