list: kill list_force_poison()

Given we have uninitialized list_heads being passed to list_add() it
will always be the case that those uninitialized values randomly trigger
the poison value.  Especially since a list_add() operation will seed the
stack with the poison value for later stack allocations to trip over.

For example, see these two false positive reports:

  list_add attempted on force-poisoned entry
  WARNING: at lib/list_debug.c:34
  [..]
  NIP [c00000000043c390] __list_add+0xb0/0x150
  LR [c00000000043c38c] __list_add+0xac/0x150
  Call Trace:
    __list_add+0xac/0x150 (unreliable)
    __down+0x4c/0xf8
    down+0x68/0x70
    xfs_buf_lock+0x4c/0x150 [xfs]

  list_add attempted on force-poisoned entry(0000000000000500),
   new->next == d0000000059ecdb0, new->prev == 0000000000000500
  WARNING: at lib/list_debug.c:33
  [..]
  NIP [c00000000042db78] __list_add+0xa8/0x140
  LR [c00000000042db74] __list_add+0xa4/0x140
  Call Trace:
    __list_add+0xa4/0x140 (unreliable)
    rwsem_down_read_failed+0x6c/0x1a0
    down_read+0x58/0x60
    xfs_log_commit_cil+0x7c/0x600 [xfs]

Fixes: commit 5c2c2587b132 ("mm, dax, pmem: introduce {get|put}_dev_pagemap() for dax-gup")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reported-by: Eryu Guan <eguan@redhat.com>
Tested-by: Eryu Guan <eguan@redhat.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/memremap.c b/kernel/memremap.c
index b981a7b023f0..778191e3e887 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -351,8 +351,13 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
         for_each_device_pfn(pfn, page_map) {
                 struct page *page = pfn_to_page(pfn);
 
-                /* ZONE_DEVICE pages must never appear on a slab lru */
-                list_force_poison(&page->lru);
+                /*
+                 * ZONE_DEVICE pages union ->lru with a ->pgmap back
+                 * pointer.  It is a bug if a ZONE_DEVICE page is ever
+                 * freed or placed on a driver-private list.  Seed the
+                 * storage with LIST_POISON* values.
+                 */
+                list_del(&page->lru);
                 page->pgmap = pgmap;
         }
         devres_add(dev, page_map);