Subject: Re: [PATCH v3 07/26] mm: drop CONFIG_HAVE_ARCH_NODEDATA_EXTENSION

From: Mike Rapoport <[email-masked]>
Date: Sun, 4 Aug 2024 10:24:15 +0300

On Sat, Aug 03, 2024 at 11:58:13AM -0700, Andrew Morton wrote:
> On Fri, 2 Aug 2024 10:49:22 +0100 Jonathan Cameron <[email-masked]> wrote:
> 
> > > --- a/mm/mm_init.c
> > > +++ b/mm/mm_init.c
> > > @@ -1838,11 +1838,10 @@ void __init free_area_init(unsigned long *max_zone_pfn)
> > >  
> > >  		if (!node_online(nid)) {
> > >  			/* Allocator not initialized yet */
> > > -			pgdat = arch_alloc_nodedata(nid);
> > > +			pgdat = memblock_alloc(sizeof(*pgdat), SMP_CACHE_BYTES);
> > >  			if (!pgdat)
> > >  				panic("Cannot allocate %zuB for node %d.\n",
> > >  				       sizeof(*pgdat), nid);
> > > -			arch_refresh_nodedata(nid, pgdat);
> > 
> > This allocates pgdat but never sets node_data[nid] to it
> > and promptly leaks it on the line below. 
> > 
> > Just to sanity check this I spun up a qemu machine with no memory
> > initially present on some nodes and it went boom as you'd expect.
> > 
> > I tested with addition of
> > 			NODE_DATA(nid) = pgdat;
> > and it all seems to work as expected.
> 
> Thanks, I added that.  It blew up on x86_64 allnoconfig because
> node_data[] (and hence NODE_DATA()) isn't an lvalue when CONFIG_NUMA=n.
> 
> I'll put some #ifdef CONFIG_NUMAs in there for now but
> 
> a) NODE_DATA() is upper-case. Implies "constant".  Shouldn't be assigned to.
> 
> b) NODE_DATA() should be non-lvalue when CONFIG_NUMA=y also.  But no,
>    we insist on implementing things in cpp instead of in C.

This looks like a candidate for a separate tree-wide cleanup.
 
> c) In fact assigning to anything which ends in "()" is nuts.  Please
>    clean up my tempfix.
> 
> c) Mike, generally I'm wondering if there's a bunch of code here
>    which isn't needed on CONFIG_NUMA=n.  Please check all of this for
>    unneeded bloatiness.

I believe the patch addresses your concerns, just with this the commit log
needs update. Instead of 

    Replace the call to arch_alloc_nodedata() in free_area_init() with
    memblock_alloc(), remove arch_refresh_nodedata() and cleanup
    include/linux/memory_hotplug.h from the associated ifdefery.

it should be

    Replace the call to arch_alloc_nodedata() in free_area_init() with a
    new helper alloc_offline_node_data(), remove arch_refresh_nodedata()
    and cleanup include/linux/memory_hotplug.h from the associated
    ifdefery.

I can send an updated patch if you prefer.

diff --git a/include/linux/numa.h b/include/linux/numa.h
index 3b12d8ca0afd..5a749fd67f39 100644
--- a/include/linux/numa.h
+++ b/include/linux/numa.h
@@ -34,6 +34,7 @@ extern struct pglist_data *node_data[];
 #define NODE_DATA(nid)	(node_data[nid])
 
 void __init alloc_node_data(int nid);
+void __init alloc_offline_node_data(int nit);
 
 /* Generic implementation available */
 int numa_nearest_node(int node, unsigned int state);
@@ -62,6 +63,8 @@ static inline int phys_to_target_node(u64 start)
 {
 	return 0;
 }
+
+static inline void alloc_offline_node_data(int nit) {}
 #endif
 
 #define numa_map_to_online_node(node) numa_nearest_node(node, N_ONLINE)
diff --git a/mm/mm_init.c b/mm/mm_init.c
index bcc2f2dd8021..2785be04e7bb 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1836,13 +1836,8 @@ void __init free_area_init(unsigned long *max_zone_pfn)
 	for_each_node(nid) {
 		pg_data_t *pgdat;
 
-		if (!node_online(nid)) {
-			/* Allocator not initialized yet */
-			pgdat = memblock_alloc(sizeof(*pgdat), SMP_CACHE_BYTES);
-			if (!pgdat)
-				panic("Cannot allocate %zuB for node %d.\n",
-				       sizeof(*pgdat), nid);
-		}
+		if (!node_online(nid))
+			alloc_offline_node_data(nid);
 
 		pgdat = NODE_DATA(nid);
 		free_area_init_node(nid);
diff --git a/mm/numa.c b/mm/numa.c
index da27eb151dc5..07e486a977c7 100644
--- a/mm/numa.c
+++ b/mm/numa.c
@@ -34,6 +34,18 @@ void __init alloc_node_data(int nid)
 	memset(NODE_DATA(nid), 0, sizeof(pg_data_t));
 }
 
+void __init alloc_offline_node_data(int nit)
+{
+	pg_data_t *pgdat;
+
+	pgdat = memblock_alloc(sizeof(*pgdat), SMP_CACHE_BYTES);
+	if (!pgdat)
+		panic("Cannot allocate %zuB for node %d.\n",
+		      sizeof(*pgdat), nid);
+
+	node_data[nid] = pgdat;
+}
+
 /* Stub functions: */
 
 #ifndef memory_add_physaddr_to_nid

-- 
Sincerely yours,
Mike.