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Date: Thu, 2 Nov 2017 13:02:21 -0400
From: Pavel Tatashin <pasha.tatashin@...cle.com>
To: steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
akpm@...ux-foundation.org, mgorman@...hsingularity.net,
mhocko@...e.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/1] mm: buddy page accessed before initialized
This problem is seen when machine is rebooted after kexec:
A message like this is printed:
==========================================================================
WARNING: CPU: 21 PID: 249 at linux/lib/list_debug.c:53__listd+0x83/0xa0
Modules linked in:
CPU: 21 PID: 249 Comm: pgdatinit0 Not tainted 4.14.0-rc6_pt_deferred #90
Hardware name: Oracle Corporation ORACLE SERVER X6-2/ASM,MOTHERBOARD,1U,
BIOS 3016
node 1 initialised, 32444607 pages in 1679ms
task: ffff880180e75a00 task.stack: ffffc9000cdb0000
RIP: 0010:__list_del_entry_valid+0x83/0xa0
RSP: 0000:ffffc9000cdb3d18 EFLAGS: 00010046
RAX: 0000000000000054 RBX: 0000000000000009 RCX: ffffffff81c5f3e8
RDX: 0000000000000000 RSI: 0000000000000086 RDI: 0000000000000046
RBP: ffffc9000cdb3d18 R08: 00000000fffffffe R09: 0000000000000154
R10: 0000000000000005 R11: 0000000000000153 R12: 0000000001fcdc00
R13: 0000000001fcde00 R14: ffff88207ffded00 R15: ffffea007f370000
FS: 0000000000000000(0000) GS:ffff881fffac0000(0000) knlGS:0
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000407ec09001 CR4: 00000000003606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
free_one_page+0x103/0x390
__free_pages_ok+0x1cf/0x2d0
__free_pages+0x19/0x30
__free_pages_boot_core+0xae/0xba
deferred_free_range+0x60/0x94
deferred_init_memmap+0x324/0x372
kthread+0x109/0x140
? __free_pages_bootmem+0x2e/0x2e
? kthread_park+0x60/0x60
ret_from_fork+0x25/0x30
list_del corruption. next->prev should be ffffea007f428020, but was
ffffea007f1d8020
==========================================================================
The problem happens in this path:
page_alloc_init_late
deferred_init_memmap
deferred_init_range
__def_free
deferred_free_range
__free_pages_boot_core(page, order)
__free_pages()
__free_pages_ok()
free_one_page()
__free_one_page(page, pfn, zone, order, migratetype);
deferred_init_range() initializes one page at a time by calling
__init_single_page(), once it initializes pageblock_nr_pages pages, it
calls deferred_free_range() to free the initialized pages to the buddy
allocator. Eventually, we reach __free_one_page(), where we compute buddy
page:
buddy_pfn = __find_buddy_pfn(pfn, order);
buddy = page + (buddy_pfn - pfn);
buddy_pfn is computed as pfn ^ (1 << order), or pfn + pageblock_nr_pages.
Thefore, buddy page becomes a page one after the range that currently was
initialized, and we access this page in this function. Also, later when we
return back to deferred_init_range(), the buddy page is initialized again.
So, in order to avoid this issue, we must initialize the buddy page prior
to calling deferred_free_range().
Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
---
mm/page_alloc.c | 66 +++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 43 insertions(+), 23 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 97687b38da05..201bf67ce042 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1449,9 +1449,9 @@ static inline void __init pgdat_init_report_one_done(void)
* Helper for deferred_init_range, free the given range, reset the counters, and
* return number of pages freed.
*/
-static inline unsigned long __def_free(unsigned long *nr_free,
- unsigned long *free_base_pfn,
- struct page **page)
+static inline unsigned long __init __def_free(unsigned long *nr_free,
+ unsigned long *free_base_pfn,
+ struct page **page)
{
unsigned long nr = *nr_free;
@@ -1463,8 +1463,9 @@ static inline unsigned long __def_free(unsigned long *nr_free,
return nr;
}
-static unsigned long deferred_init_range(int nid, int zid, unsigned long pfn,
- unsigned long end_pfn)
+static unsigned long __init deferred_init_range(int nid, int zid,
+ unsigned long start_pfn,
+ unsigned long end_pfn)
{
struct mminit_pfnnid_cache nid_init_state = { };
unsigned long nr_pgmask = pageblock_nr_pages - 1;
@@ -1472,23 +1473,44 @@ static unsigned long deferred_init_range(int nid, int zid, unsigned long pfn,
unsigned long nr_pages = 0;
unsigned long nr_free = 0;
struct page *page = NULL;
+ unsigned long pfn;
- for (; pfn < end_pfn; pfn++) {
- /*
- * First we check if pfn is valid on architectures where it is
- * possible to have holes within pageblock_nr_pages. On systems
- * where it is not possible, this function is optimized out.
- *
- * Then, we check if a current large page is valid by only
- * checking the validity of the head pfn.
- *
- * meminit_pfn_in_nid is checked on systems where pfns can
- * interleave within a node: a pfn is between start and end
- * of a node, but does not belong to this memory node.
- *
- * Finally, we minimize pfn page lookups and scheduler checks by
- * performing it only once every pageblock_nr_pages.
- */
+ /*
+ * First we check if pfn is valid on architectures where it is possible
+ * to have holes within pageblock_nr_pages. On systems where it is not
+ * possible, this function is optimized out.
+ *
+ * Then, we check if a current large page is valid by only checking the
+ * validity of the head pfn.
+ *
+ * meminit_pfn_in_nid is checked on systems where pfns can interleave
+ * within a node: a pfn is between start and end of a node, but does not
+ * belong to this memory node.
+ *
+ * Finally, we minimize pfn page lookups and scheduler checks by
+ * performing it only once every pageblock_nr_pages.
+ *
+ * We do it in two loops: first we initialize struct page, than free to
+ * buddy allocator, becuse while we are freeing pages we can access
+ * pages that are ahead (computing buddy page in __free_one_page()).
+ */
+ for (pfn = start_pfn; pfn < end_pfn; pfn++) {
+ if (!pfn_valid_within(pfn))
+ continue;
+ if ((pfn & nr_pgmask) || pfn_valid(pfn)) {
+ if (meminit_pfn_in_nid(pfn, nid, &nid_init_state)) {
+ if (page && (pfn & nr_pgmask))
+ page++;
+ else
+ page = pfn_to_page(pfn);
+ __init_single_page(page, pfn, zid, nid);
+ cond_resched();
+ }
+ }
+ }
+
+ page = NULL;
+ for (pfn = start_pfn; pfn < end_pfn; pfn++) {
if (!pfn_valid_within(pfn)) {
nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
} else if (!(pfn & nr_pgmask) && !pfn_valid(pfn)) {
@@ -1497,12 +1519,10 @@ static unsigned long deferred_init_range(int nid, int zid, unsigned long pfn,
nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
} else if (page && (pfn & nr_pgmask)) {
page++;
- __init_single_page(page, pfn, zid, nid);
nr_free++;
} else {
nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
page = pfn_to_page(pfn);
- __init_single_page(page, pfn, zid, nid);
free_base_pfn = pfn;
nr_free = 1;
cond_resched();
--
2.15.0
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