mm/memory_hotplug: don't access uninitialized memmaps in shrink_pgdat_span()

We might use the nid of memmaps that were never initialized.  For
example, if the memmap was poisoned, we will crash the kernel in
pfn_to_nid() right now.  Let's use the calculated boundaries of the
separate zones instead.  This now also avoids having to iterate over a
whole bunch of subsections again, after shrinking one zone.

Before commit d0dc12e86b31 ("mm/memory_hotplug: optimize memory
hotplug"), the memmap was initialized to 0 and the node was set to the
right value.  After that commit, the node might be garbage.

We'll have to fix shrink_zone_span() next.

Link: http://lkml.kernel.org/r/20191006085646.5768-4-david@redhat.com
Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online")	[d0dc12e86b319]
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Damian Tometzki <damian.tometzki@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jun Yao <yaojun8558363@gmail.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Pankaj Gupta <pagupta@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pavel Tatashin <pavel.tatashin@microsoft.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qian Cai <cai@lca.pw>
Cc: Rich Felker <dalias@libc.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Steve Capper <steve.capper@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>	[4.13+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 57 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index b1be791f772d..df570e5c71cc 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -436,67 +436,25 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
         zone_span_writeunlock(zone);
 }
 
-static void shrink_pgdat_span(struct pglist_data *pgdat,
-                              unsigned long start_pfn, unsigned long end_pfn)
+static void update_pgdat_span(struct pglist_data *pgdat)
 {
-        unsigned long pgdat_start_pfn = pgdat->node_start_pfn;
-        unsigned long p = pgdat_end_pfn(pgdat); /* pgdat_end_pfn namespace clash */
-        unsigned long pgdat_end_pfn = p;
-        unsigned long pfn;
-        int nid = pgdat->node_id;
-
-        if (pgdat_start_pfn == start_pfn) {
-                /*
-                 * If the section is smallest section in the pgdat, it need
-                 * shrink pgdat->node_start_pfn and pgdat->node_spanned_pages.
-                 * In this case, we find second smallest valid mem_section
-                 * for shrinking zone.
-                 */
-                pfn = find_smallest_section_pfn(nid, NULL, end_pfn,
-                                                pgdat_end_pfn);
-                if (pfn) {
-                        pgdat->node_start_pfn = pfn;
-                        pgdat->node_spanned_pages = pgdat_end_pfn - pfn;
-                }
-        } else if (pgdat_end_pfn == end_pfn) {
-                /*
-                 * If the section is biggest section in the pgdat, it need
-                 * shrink pgdat->node_spanned_pages.
-                 * In this case, we find second biggest valid mem_section for
-                 * shrinking zone.
-                 */
-                pfn = find_biggest_section_pfn(nid, NULL, pgdat_start_pfn,
-                                               start_pfn);
-                if (pfn)
-                        pgdat->node_spanned_pages = pfn - pgdat_start_pfn + 1;
-        }
-
-        /*
-         * If the section is not biggest or smallest mem_section in the pgdat,
-         * it only creates a hole in the pgdat. So in this case, we need not
-         * change the pgdat.
-         * But perhaps, the pgdat has only hole data. Thus it check the pgdat
-         * has only hole or not.
-         */
-        pfn = pgdat_start_pfn;
-        for (; pfn < pgdat_end_pfn; pfn += PAGES_PER_SUBSECTION) {
-                if (unlikely(!pfn_valid(pfn)))
-                        continue;
-
-                if (pfn_to_nid(pfn) != nid)
-                        continue;
+        unsigned long node_start_pfn = 0, node_end_pfn = 0;
+        struct zone *zone;
 
-                /* Skip range to be removed */
-                if (pfn >= start_pfn && pfn < end_pfn)
-                        continue;
+        for (zone = pgdat->node_zones;
+             zone < pgdat->node_zones + MAX_NR_ZONES; zone++) {
+                unsigned long zone_end_pfn = zone->zone_start_pfn +
+                                             zone->spanned_pages;
 
-                /* If we find valid section, we have nothing to do */
-                return;
+                /* No need to lock the zones, they can't change. */
+                if (zone_end_pfn > node_end_pfn)
+                        node_end_pfn = zone_end_pfn;
+                if (zone->zone_start_pfn < node_start_pfn)
+                        node_start_pfn = zone->zone_start_pfn;
         }
 
-        /* The pgdat has no valid section */
-        pgdat->node_start_pfn = 0;
-        pgdat->node_spanned_pages = 0;
+        pgdat->node_start_pfn = node_start_pfn;
+        pgdat->node_spanned_pages = node_end_pfn - node_start_pfn;
 }
 
 static void __remove_zone(struct zone *zone, unsigned long start_pfn,
@@ -507,7 +465,7 @@ static void __remove_zone(struct zone *zone, unsigned long start_pfn,
 
         pgdat_resize_lock(zone->zone_pgdat, &flags);
         shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
-        shrink_pgdat_span(pgdat, start_pfn, start_pfn + nr_pages);
+        update_pgdat_span(pgdat);
         pgdat_resize_unlock(zone->zone_pgdat, &flags);
 }