mm: don't panic when links can't be created in sysfs

At boot time, or when doing memory hot-add operations, if the links in
sysfs can't be created, the system is still able to run, so just report
the error in the kernel log rather than BUG_ON and potentially make system
unusable because the callpath can be called with locks held.

Since the number of memory blocks managed could be high, the messages are
rate limited.

As a consequence, link_mem_sections() has no status to report anymore.

Signed-off-by: Laurent Dufour <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Reviewed-by: Oscar Salvador <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Fenghua Yu <[e-mail]>
Cc: Nathan Lynch <[e-mail]>
Cc: "Rafael J . Wysocki" <[e-mail]>
Cc: Scott Cheloha <[e-mail]>
Cc: Tony Luck <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/base/node.c

···
 	return pfn_to_nid(pfn);
 }
 
-static int do_register_memory_block_under_node(int nid,
-					       struct memory_block *mem_blk)
+static void do_register_memory_block_under_node(int nid,
+						struct memory_block *mem_blk)
 {
 	int ret;
 
···
 	ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
 				       &mem_blk->dev.kobj,
 				       kobject_name(&mem_blk->dev.kobj));
-	if (ret)
-		return ret;
+	if (ret && ret != -EEXIST)
+		dev_err_ratelimited(&node_devices[nid]->dev,
+				    "can't create link to %s in sysfs (%d)\n",
+				    kobject_name(&mem_blk->dev.kobj), ret);
 
-	return sysfs_create_link_nowarn(&mem_blk->dev.kobj,
+	ret = sysfs_create_link_nowarn(&mem_blk->dev.kobj,
 				&node_devices[nid]->dev.kobj,
 				kobject_name(&node_devices[nid]->dev.kobj));
+	if (ret && ret != -EEXIST)
+		dev_err_ratelimited(&mem_blk->dev,
+				    "can't create link to %s in sysfs (%d)\n",
+				    kobject_name(&node_devices[nid]->dev.kobj),
+				    ret);
 }
 
 /* register memory section under specified node if it spans that node */
···
 		if (page_nid != nid)
 			continue;
 
-		return do_register_memory_block_under_node(nid, mem_blk);
+		do_register_memory_block_under_node(nid, mem_blk);
+		return 0;
 	}
 	/* mem section does not span the specified node */
 	return 0;
···
 {
 	int nid = *(int *)arg;
 
-	return do_register_memory_block_under_node(nid, mem_blk);
+	do_register_memory_block_under_node(nid, mem_blk);
+	return 0;
 }
 
 /*
···
 			  kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
 }
 
-int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
-		      enum meminit_context context)
+void link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn,
+		       enum meminit_context context)
 {
 	walk_memory_blocks_func_t func;
 
···
 	else
 		func = register_mem_block_under_node_early;
 
-	return walk_memory_blocks(PFN_PHYS(start_pfn),
-				  PFN_PHYS(end_pfn - start_pfn), (void *)&nid,
-				  func);
+	walk_memory_blocks(PFN_PHYS(start_pfn), PFN_PHYS(end_pfn - start_pfn),
+			   (void *)&nid, func);
+	return;
 }
 
 #ifdef CONFIG_HUGETLBFS

include/linux/node.h

···
 typedef  void (*node_registration_func_t)(struct node *);
 
 #if defined(CONFIG_MEMORY_HOTPLUG_SPARSE) && defined(CONFIG_NUMA)
-int link_mem_sections(int nid, unsigned long start_pfn,
-		      unsigned long end_pfn,
-		      enum meminit_context context);
+void link_mem_sections(int nid, unsigned long start_pfn,
+		       unsigned long end_pfn,
+		       enum meminit_context context);
 #else
-static inline int link_mem_sections(int nid, unsigned long start_pfn,
-				    unsigned long end_pfn,
-				    enum meminit_context context)
+static inline void link_mem_sections(int nid, unsigned long start_pfn,
+				     unsigned long end_pfn,
+				     enum meminit_context context)
 {
-	return 0;
 }
 #endif
 
···
 		if (error)
 			return error;
 		/* link memory sections under this node */
-		error = link_mem_sections(nid, start_pfn, end_pfn,
-					  MEMINIT_EARLY);
+		link_mem_sections(nid, start_pfn, end_pfn, MEMINIT_EARLY);
 	}
 
 	return error;

mm/memory_hotplug.c

···
 	}
 
 	/* link memory sections under this node.*/
-	ret = link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1),
-				MEMINIT_HOTPLUG);
-	BUG_ON(ret);
+	link_mem_sections(nid, PFN_DOWN(start), PFN_UP(start + size - 1),
+			  MEMINIT_HOTPLUG);
 
 	/* create new memmap entry */
 	if (!strcmp(res->name, "System RAM"))