powerpc/powernv: hold device_hotplug_lock when calling memtrace_offline_pages()

Let's perform all checking + offlining + removing under
device_hotplug_lock, so nobody can mess with these devices via sysfs
concurrently.

[david@redhat.com: take device_hotplug_lock outside of loop]
  Link: http://lkml.kernel.org/r/20180927092554.13567-6-david@redhat.com
Link: http://lkml.kernel.org/r/20180925091457.28651-6-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
Reviewed-by: Rashmica Gupta <rashmica.g@gmail.com>
Acked-by: Balbir Singh <bsingharora@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Rashmica Gupta <rashmica.g@gmail.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: John Allen <jallen@linux.vnet.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Mathieu Malaterre <malat@debian.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/platforms/powernv/memtrace.c

@@ -70,6 +70,7 @@ static int change_memblock_state(struct memory_block *mem, void *arg)
 	return 0;
 }
 
+/* called with device_hotplug_lock held */
 static bool memtrace_offline_pages(u32 nid, u64 start_pfn, u64 nr_pages)
 {
 	u64 end_pfn = start_pfn + nr_pages - 1;
@@ -110,6 +111,7 @@ static u64 memtrace_alloc_node(u32 nid, u64 size)
 	/* Trace memory needs to be aligned to the size */
 	end_pfn = round_down(end_pfn - nr_pages, nr_pages);
 
+	lock_device_hotplug();
 	for (base_pfn = end_pfn; base_pfn > start_pfn; base_pfn -= nr_pages) {
 		if (memtrace_offline_pages(nid, base_pfn, nr_pages) == true) {
 			/*
@@ -118,7 +120,6 @@ static u64 memtrace_alloc_node(u32 nid, u64 size)
 			 * we never try to remove memory that spans two iomem
 			 * resources.
 			 */
-			lock_device_hotplug();
 			end_pfn = base_pfn + nr_pages;
 			for (pfn = base_pfn; pfn < end_pfn; pfn += bytes>> PAGE_SHIFT) {
 				__remove_memory(nid, pfn << PAGE_SHIFT, bytes);
@@ -127,6 +128,7 @@ static u64 memtrace_alloc_node(u32 nid, u64 size)
 			return base_pfn << PAGE_SHIFT;
 		}
 	}
+	unlock_device_hotplug();
 
 	return 0;
 }