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

[Vlastimil Babka]

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 at linux-foundation.org>
>> Cc: linux-mm at kvack.org
>> Cc: Mel Gorman <mgorman at suse.de>
>> Cc: Michael Ellerman <mpe at ellerman.id.au>
>> Cc: Sachin Sant <sachinp at linux.vnet.ibm.com>
>> Cc: Michal Hocko <mhocko at kernel.org>
>> Cc: Christopher Lameter <cl at linux.com>
>> Cc: linuxppc-dev at lists.ozlabs.org
>> Cc: Joonsoo Kim <iamjoonsoo.kim at lge.com>
>> Cc: Kirill Tkhai <ktkhai at virtuozzo.com>
>> Cc: Vlastimil Babka <vbabka at suse.cz>
>> Cc: Srikar Dronamraju <srikar at linux.vnet.ibm.com>
>> Cc: Bharata B Rao <bharata at linux.ibm.com>
>> Cc: Nathan Lynch <nathanl at linux.ibm.com>
>> 
>> Reported-by: Sachin Sant <sachinp at linux.vnet.ibm.com>
>> Tested-by: Sachin Sant <sachinp at linux.vnet.ibm.com>
>> Signed-off-by: Srikar Dronamraju <srikar at 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

----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))
 		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
+		 * ignore the constraint
+		 */
+		if ((!node_online(node) || !node_present_pages(node))) {
+			node = NUMA_NO_NODE;
+			goto redo;
+		} else {
 			stat(s, ALLOC_NODE_MISMATCH);
 			deactivate_slab(s, page, c->freelist, c);
 			goto new_slab;