mm: bootmem: fix free_all_bootmem_core() with odd bitmap alignment

Currently free_all_bootmem_core ignores that node_min_pfn may be not
multiple of BITS_PER_LONG.  Eg commit 6dccdcbe2c3e ("mm: bootmem: fix
checking the bitmap when finally freeing bootmem") shifts vec by lower
bits of start instead of lower bits of idx.  Also

  if (IS_ALIGNED(start, BITS_PER_LONG) && vec == ~0UL)

assumes that vec bit 0 corresponds to start pfn, which is only true when
node_min_pfn is a multiple of BITS_PER_LONG.  Also loop in the else
clause can double-free pages (e.g.  with node_min_pfn == start == 1,
map[0] == ~0 on 32-bit machine page 32 will be double-freed).

This bug causes the following message during xtensa kernel boot:

  bootmem::free_all_bootmem_core nid=0 start=1 end=8000
  BUG: Bad page state in process swapper  pfn:00001
  page:d04bd020 count:0 mapcount:-127 mapping:  (null) index:0x2
  page flags: 0x0()
  Call Trace:
    bad_page+0x8c/0x9c
    free_pages_prepare+0x5e/0x88
    free_hot_cold_page+0xc/0xa0
    __free_pages+0x24/0x38
    __free_pages_bootmem+0x54/0x56
    free_all_bootmem_core$part$11+0xeb/0x138
    free_all_bootmem+0x46/0x58
    mem_init+0x25/0xa4
    start_kernel+0x11e/0x25c
    should_never_return+0x0/0x3be7

The fix is the following:
 - always align vec so that its bit 0 corresponds to start
 - provide BITS_PER_LONG bits in vec, if those bits are available in the
   map
 - don't free pages past next start position in the else clause.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Cc: Gavin Shan <shangw@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Prasad Koya <prasad.koya@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 6 deletions

diff --git a/mm/bootmem.c b/mm/bootmem.c
index 1324cd74faec..b93376c39b61 100644
--- a/mm/bootmem.c
+++ b/mm/bootmem.c
@@ -185,10 +185,23 @@ static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
 
         while (start < end) {
                 unsigned long *map, idx, vec;
+                unsigned shift;
 
                 map = bdata->node_bootmem_map;
                 idx = start - bdata->node_min_pfn;
+                shift = idx & (BITS_PER_LONG - 1);
+                /*
+                 * vec holds at most BITS_PER_LONG map bits,
+                 * bit 0 corresponds to start.
+                 */
                 vec = ~map[idx / BITS_PER_LONG];
+
+                if (shift) {
+                        vec >>= shift;
+                        if (end - start >= BITS_PER_LONG)
+                                vec |= ~map[idx / BITS_PER_LONG + 1] <<
+                                        (BITS_PER_LONG - shift);
+                }
                 /*
                  * If we have a properly aligned and fully unreserved
                  * BITS_PER_LONG block of pages in front of us, free
@@ -201,19 +214,18 @@ static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
                         count += BITS_PER_LONG;
                         start += BITS_PER_LONG;
                 } else {
-                        unsigned long off = 0;
+                        unsigned long cur = start;
 
-                        vec >>= start & (BITS_PER_LONG - 1);
-                        while (vec) {
+                        start = ALIGN(start + 1, BITS_PER_LONG);
+                        while (vec && cur != start) {
                                 if (vec & 1) {
-                                        page = pfn_to_page(start + off);
+                                        page = pfn_to_page(cur);
                                         __free_pages_bootmem(page, 0);
                                         count++;
                                 }
                                 vec >>= 1;
-                                off++;
+                                ++cur;
                         }
-                        start = ALIGN(start + 1, BITS_PER_LONG);
                 }
         }