Has this been reviewed properly? I do not see any Acks nor Reviewed-bys. Did Aneesh gave it some testing?

On Fri 18-10-19 20:19:33, Andrew Morton wrote:

From: David Hildenbrand david@redhat.com Subject: 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

---

mm/memory_hotplug.c | 74 +++++++++--------------------------------- 1 file changed, 16 insertions(+), 58 deletions(-)

--- a/mm/memory_hotplug.c~mm-memory_hotplug-dont-access-uninitialized-memmaps-in-shrink_pgdat_span +++ a/mm/memory_hotplug.c @@ -436,67 +436,25 @@ static void shrink_zone_span(struct zone 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;
  

• /* Skip range to be removed */
  

• if (pfn >= start_pfn && pfn < end_pfn)
  

• 	continue;
  

• unsigned long node_start_pfn = 0, node_end_pfn = 0;
• struct zone *zone;

• /* If we find valid section, we have nothing to do */
  

• return;
  

• 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;
  

• /* 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 *z 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);

} _