Re: [PATCH 1/3] mm: munlock: fix a bug where THP tail page is encountered
From: Vlastimil Babka
Date: Mon Mar 17 2014 - 19:30:37 EST
On 17.3.2014 23:58, Sasha Levin wrote:
On 03/17/2014 06:20 PM, Vlastimil Babka wrote:
On 17.3.2014 22:08, Sasha Levin wrote:
On 03/17/2014 08:38 AM, Vlastimil Babka wrote:
On 03/15/2014 04:06 AM, Sasha Levin wrote:
On 03/14/2014 07:55 PM, Sasha Levin wrote:
On 12/17/2013 08:00 AM, Vlastimil Babka wrote:
From: Vlastimil Babka<vbabka@xxxxxxx>
Date: Fri, 13 Dec 2013 14:25:21 +0100
Subject: [PATCH 1/3] mm: munlock: fix a bug where THP tail page
is encountered
Since commit ff6a6da60 ("mm: accelerate munlock() treatment of
THP pages")
munlock skips tail pages of a munlocked THP page. However, when
the head page
already has PageMlocked unset, it will not skip the tail pages.
Commit 7225522bb ("mm: munlock: batch non-THP page isolation and
munlock+putback using pagevec") has added a PageTransHuge()
check which
contains VM_BUG_ON(PageTail(page)). Sasha Levin found this
triggered using
trinity, on the first tail page of a THP page without
PageMlocked flag.
This patch fixes the issue by skipping tail pages also in the
case when
PageMlocked flag is unset. There is still a possibility of race
with THP page
split between clearing PageMlocked and determining how many
pages to skip.
The race might result in former tail pages not being skipped,
which is however
no longer a bug, as during the skip the PageTail flags are cleared.
However this race also affects correctness of NR_MLOCK
accounting, which is to
be fixed in a separate patch.
I've hit the same thing again, on the latest -next, this time
with a different trace:
[ 539.199120] page:ffffea0013249a80 count:0 mapcount:1
mapping: (null) index:0x0
[ 539.200429] page flags: 0x12fffff80008000(tail)
[ 539.201167] ------------[ cut here ]------------
[ 539.201889] kernel BUG at include/linux/page-flags.h:415!
[ 539.202859] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 539.204588] Dumping ftrace buffer:
[ 539.206415] (ftrace buffer empty)
[ 539.207022] Modules linked in:
[ 539.207503] CPU: 3 PID: 18262 Comm: trinity-c228 Tainted:
G W 3.14.0-rc6-next-20140313-sasha-00010-gb8c1db1-dirty #217
[ 539.209012] task: ffff880627b10000 ti: ffff8805a44c2000
task.ti: ffff8805a44c2000
[ 539.209989] RIP: munlock_vma_pages_range+0x93/0x1d0
(include/linux/page-flags.h:415 mm/mlock.c:494)
[ 539.210263] RSP: 0000:ffff8805a44c3e08 EFLAGS: 00010246
[ 539.210263] RAX: ffff88052ae126a0 RBX: 000000000006a000 RCX:
0000000000000099
[ 539.210263] RDX: 0000000000000000 RSI: ffff880627b10cf0 RDI:
0000000004c926a0
[ 539.210263] RBP: ffff8805a44c3ec8 R08: 0000000000000001 R09:
0000000000000001
[ 539.210263] R10: 0000000000000001 R11: 0000000000000001 R12:
ffffea0013249a80
[ 539.210263] R13: ffff88039dc95a00 R14: 000000000006b000 R15:
ffff8805a44c3e94
[ 539.210263] FS: 00007fd6ce14a700(0000)
GS:ffff88042b800000(0000) knlGS:0000000000000000
[ 539.210263] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 539.210263] CR2: 00007fd6ce0ef6ac CR3: 00000006025cd000 CR4:
00000000000006a0
[ 539.210263] DR0: 0000000000698000 DR1: 0000000000000000 DR2:
0000000000000000
[ 539.210263] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
0000000000000600
[ 539.210263] Stack:
[ 539.210263] 0000000000000000 0000000000000000
00018805a44c3e38 0000000000000000
[ 539.210263] 0000000000000000 ffff88039dc95a00
00000000a44c3e88 0000000000000000
[ 539.210263] 00ff8805a44c3e58 ffff880528f0a0f0
ffff8805a44c3eb8 ffff88039dc95a00
[ 539.210263] Call Trace:
[ 539.210263] do_munmap+0x1d2/0x360 (mm/internal.h:168
mm/mmap.c:2547)
[ 539.210263] ? down_write+0xa6/0xc0 (kernel/locking/rwsem.c:51)
[ 539.210263] ? vm_munmap+0x46/0x80 (mm/mmap.c:2571)
[ 539.210263] vm_munmap+0x54/0x80 (mm/mmap.c:2572)
[ 539.210263] SyS_munmap+0x2c/0x40 (mm/mmap.c:2577)
[ 539.210263] tracesys+0xdd/0xe2 (arch/x86/kernel/entry_64.S:749)
[ 539.210263] Code: ff 49 89 c4 48 85 c0 0f 84 f3 00 00 00 48 3d
00 f0 ff ff 0f 87 e7 00 00 00 48 8b 00 66 85 c0 79 17 31 f6 4c 89
e7 e8 4d d2 fc ff <0f> 0b 0f 1f 00 eb fe 66 0f 1f 44 00 00 49 8b
04 24 f6 c4 40 74
[ 539.210263] RIP munlock_vma_pages_range+0x93/0x1d0
(include/linux/page-flags.h:415 mm/mlock.c:494)
[ 539.210263] RSP <ffff8805a44c3e08>
[ 539.236666] ---[ end trace 4e90dc9141579181 ]---
Thanks,
Sasha
And another related trace:
[ 741.192502] kernel BUG at mm/mlock.c:528!
[ 741.193088] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 741.194177] Dumping ftrace buffer:
[ 741.194645] (ftrace buffer empty)
[ 741.195109] Modules linked in:
[ 741.195728] CPU: 23 PID: 19908 Comm: trinity-c264 Tainted:
G W 3.14.0-rc6-next-20140314-sasha-00012-g5590866 #219
[ 741.197549] task: ffff88061fc2b000 ti: ffff8805decb8000
task.ti: ffff8805decb8000
[ 741.198548] RIP: munlock_vma_pages_range+0x176/0x1d0
(mm/mlock.c:528)
[ 741.199754] RSP: 0018:ffff8805decb9e08 EFLAGS: 00010206
[ 741.200085] RAX: 00000000000001ff RBX: 0000000000111000 RCX:
0000000000000000
[ 741.200085] RDX: 0000000000000111 RSI: ffffffff81295fdd RDI:
ffffffff84490705
[ 741.200085] RBP: ffff8805decb9ec8 R08: 0000000000000000 R09:
0000000000000000
[ 741.200085] R10: 0000000000000001 R11: 0000000000000000 R12:
fffffffffffffff2
[ 741.200085] R13: ffff880221044e00 R14: 0000000000112000 R15:
ffff8805decb9e94
[ 741.200085] FS: 00007f4bec6bc700(0000)
GS:ffff88082ba00000(0000) knlGS:0000000000000000
[ 741.200085] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 741.200085] CR2: 0000000003109a98 CR3: 00000005decaf000 CR4:
00000000000006a0
[ 741.200085] Stack:
[ 741.200085] 0000000000000000 0000000000000000 00018805decb9e38
0000000000000000
[ 741.200085] 0000000000000000 ffff880221044e00 00000000decb9e88
0000000000000000
[ 741.200085] 00ff8805decb9e58 ffff880ff376f450 ffff8805decb9eb8
ffff880221044e00
[ 741.200085] Call Trace:
[ 741.200085] do_munmap+0x1d2/0x360 (mm/internal.h:168
mm/mmap.c:2547)
[ 741.200085] ? down_write+0xa6/0xc0 (kernel/locking/rwsem.c:51)
[ 741.200085] ? vm_munmap+0x46/0x80 (mm/mmap.c:2571)
[ 741.200085] vm_munmap+0x54/0x80 (mm/mmap.c:2572)
[ 741.200085] SyS_munmap+0x2c/0x40 (mm/mmap.c:2577)
[ 741.200085] tracesys+0xdd/0xe2 (arch/x86/kernel/entry_64.S:749)
[ 741.200085] Code: fd ff ff 4c 89 e6 48 89 c3 48 8d bd 40 ff ff
ff e8 80 fa ff ff eb 2f 66 0f 1f 44 00 00 8b 45 cc 48 89 da 48 c1
ea 0c 85 d0 74 12 <0f> 0b 0f 1f 84 00 00 00 00 00 eb fe 66 0f 1f
44 00 00 ff c0 48
[ 741.200085] RIP munlock_vma_pages_range+0x176/0x1d0
(mm/mlock.c:528)
[ 741.200085] RSP <ffff8805decb9e08>
Sigh, again? I really wonder what is it this time :)
Please try this debug patch, hopefully we learn something:
diff --git a/mm/mlock.c b/mm/mlock.c
index 4e1a6816..7094bac 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -469,12 +469,14 @@ static unsigned long
__munlock_pagevec_fill(struct pagevec *pvec,
void munlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
+ unsigned long orig_start = start;
+ unsigned long page_increm = 0;
+
vma->vm_flags &= ~VM_LOCKED;
while (start < end) {
struct page *page = NULL;
unsigned int page_mask;
- unsigned long page_increm;
struct pagevec pvec;
struct zone *zone;
int zoneid;
@@ -491,6 +493,24 @@ void munlock_vma_pages_range(struct
vm_area_struct *vma,
&page_mask);
if (page && !IS_ERR(page)) {
+ if (PageTail(page)) {
+ struct page *first_page;
+ dump_page(page, "Unexpected PageTail");
+ printk("start=%lu pfn=%lu orig_start=%lu "
+ "page_increm=%lu "
+ "vm_start=%lu vm_end=%lu vm_flags=%lu\n",
+ start, page_to_pfn(page), orig_start,
+ page_increm,
+ vma->vm_start, vma->vm_end,
+ vma->vm_flags);
+ first_page = page->first_page;
+ printk("first_page pfn=%lu\n",
+ page_to_pfn(first_page));
+ dump_page(first_page, "first_page of unexpected
PageTail page");
+ if (PageCompound(first_page))
+ printk("first_page is compound with
order=%d\n", compound_order(first_page));
+ VM_BUG_ON(true);
+ }
if (PageTransHuge(page)) {
lock_page(page);
/*
@@ -525,7 +545,25 @@ void munlock_vma_pages_range(struct
vm_area_struct *vma,
}
}
/* It's a bug to munlock in the middle of a THP page */
- VM_BUG_ON((start >> PAGE_SHIFT) & page_mask);
+ if ((start >> PAGE_SHIFT) & page_mask) {
+ dump_page(page, "unexpected middle of THP page");
+ printk("start=%lu pfn=%lu orig_start=%lu "
In this scenario page might be error or NULL, no?
Hm I doubt page_mask would be nonzero in such case, but who knows
what weirdness causes this...
Feel free to move the dump_page() below printk() so we still get
useful info before it crashes on
dump_page() in such situation.
It happened once, so I moved it, but in the meanwhile I got something
useful:
[ 1753.907376] page:ffffea0017130c40 count:0 mapcount:1
mapping: (null) index:0x2
[ 1753.908327] page flags: 0x16fffff80008000(tail)
[ 1753.908973] page dumped because: Unexpected PageTail
[ 1753.909595] start=140340826935296 pfn=6048817
orig_start=140340826935296 page_increm=0 vm_start=140340826935296
vm_end=140340826939392 vm_flags=1210057078
Uh so that looks like the vma starts in the middle of a THP page. That
doesn't look right...
In the first instance of this bug I thought of this but it didn't seem
possible. Something must have changed.
I can take closer look tomorrow.
[ 1753.911220] first_page pfn=6048768
[ 1753.911692] page:ffffea0017130000 count:2 mapcount:1
mapping:ffff880612b41f01 index:0x7fa3a5200
[ 1753.912733] page flags:
0x16fffff80384028(uptodate|lru|head|swapbacked|unevictable|mlocked)
[ 1753.913464] page dumped because: first_page of unexpected PageTail
page
[ 1753.914387] pc:ffff88062adcc000 pc->flags:2
pc->mem_cgroup:ffff88012b474520
[ 1753.914387] first_page is compound with order=9
[ 1753.914387] ------------[ cut here ]------------
[ 1753.914387] kernel BUG at mm/mlock.c:512!
[ 1753.914387] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[ 1753.914387] Dumping ftrace buffer:
[ 1753.914387] (ftrace buffer empty)
[ 1753.914387] Modules linked in:
[ 1753.914387] CPU: 26 PID: 36822 Comm: trinity-c337 Tainted: G
W 3.14.0-rc6-next-20140317-sasha-00012-ge933921-dirty #226
[ 1753.914387] task: ffff88090cdeb000 ti: ffff88090a868000 task.ti:
ffff88090a868000
[ 1753.914387] RIP: 0010:[<ffffffff8129ca7a>] [<ffffffff8129ca7a>]
munlock_vma_pages_range+0x12a/0x340
[ 1753.914387] RSP: 0018:ffff88090a869dd8 EFLAGS: 00010292
[ 1753.914387] RAX: 0000000000000023 RBX: ffffea0017130000 RCX:
0000000000000006
[ 1753.914387] RDX: 0000000000000006 RSI: ffff88090cdebcf0 RDI:
0000000000000282
[ 1753.914387] RBP: ffff88090a869ec8 R08: 0000000000000001 R09:
0000000000000001
[ 1753.914387] R10: 0000000000000001 R11: 0000000000000001 R12:
00007fa3a5231000
[ 1753.914387] R13: ffff880613c69400 R14: 0000160000000000 R15:
0000000000000000
[ 1753.914387] FS: 00007fa3a9081700(0000) GS:ffff880b2ba00000(0000)
knlGS:0000000000000000
[ 1753.914387] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 1753.914387] CR2: 0000000002fff0a8 CR3: 00000008fa08d000 CR4:
00000000000006a0
[ 1753.914387] Stack:
[ 1753.914387] 00007fa3a5232000 0000000048200176 00007fa3a552a000
ffff880613c6a800
[ 1753.914387] 00007fa3a552a000 00007fa3a5231000 0000000000000000
0000000000000000
[ 1753.914387] 000188090a869e38 0000000000000000 0000000000000000
ffff880613c69400
[ 1753.914387] Call Trace:
[ 1753.914387] [<ffffffff812a0302>] do_munmap+0x1d2/0x360
[ 1753.914387] [<ffffffff844a42e6>] ? down_write+0xa6/0xc0
[ 1753.914387] [<ffffffff812a04d6>] ? vm_munmap+0x46/0x80
[ 1753.914387] [<ffffffff812a04e4>] vm_munmap+0x54/0x80
[ 1753.914387] [<ffffffff812a053c>] SyS_munmap+0x2c/0x40
[ 1753.914387] [<ffffffff844b04d0>] tracesys+0xdd/0xe2
[ 1753.914387] Code: 85 48 89 df e8 98 d0 fc ff 66 f7 03 00 c0 74 1b
48 8b 03 31 f6 f6 c4 40 74 03 8b 73 68 48 c7 c7 58 7d 6e 85 31 c0 e8
52 1f 20 03 <0f> 0b 0f 1f 40 00 eb fe 66 0f 1f 44 00 00 48 8b 03 66 85
c0 79
[ 1753.914387] RIP [<ffffffff8129ca7a>]
munlock_vma_pages_range+0x12a/0x340
[ 1753.914387] RSP <ffff88090a869dd8>
Thanks,
Sasha
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