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, 0 insertions, 9 deletions

diff --git a/lib/list_debug.c b/lib/list_debug.c
index 3345a089ef7b..3859bf63561c 100644
--- a/lib/list_debug.c
+++ b/lib/list_debug.c
@@ -12,13 +12,6 @@
 #include <linux/kernel.h>
 #include <linux/rculist.h>
 
-static struct list_head force_poison;
-void list_force_poison(struct list_head *entry)
-{
-        entry->next = &force_poison;
-        entry->prev = &force_poison;
-}
-
 /*
  * Insert a new entry between two known consecutive entries.
  *
@@ -30,8 +23,6 @@ void __list_add(struct list_head *new,
                               struct list_head *prev,
                               struct list_head *next)
 {
-        WARN(new->next == &force_poison || new->prev == &force_poison,
-                "list_add attempted on force-poisoned entry\n");
         WARN(next->prev != prev,
                 "list_add corruption. next->prev should be "
                 "prev (%p), but was %p. (next=%p).\n",