[PATCH] mm: remove BUG_ON() from mlock_vma_page()

[Bob Liu <lliubbo@gmail.com>]

This BUG_ON() was triggered when called from try_to_unmap_cluster() which
didn't lock the page.
And it's safe to mlock_vma_page() without PageLocked, so this patch fix this
issue by removing that BUG_ON() simply.

[  253.869145] kernel BUG at mm/mlock.c:82!
[  253.869549] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[  253.870098] Dumping ftrace buffer:
[  253.870098]    (ftrace buffer empty)
[  253.870098] Modules linked in:
[  253.870098] CPU: 10 PID: 9162 Comm: trinity-child75 Tainted: G        W
3.13.0-rc4-next-20131216-sasha-00011-g5f105ec-dirty #4137
[  253.873310] task: ffff8800c98cb000 ti: ffff8804d34e8000 task.ti:
ffff8804d34e8000
[  253.873310] RIP: 0010:[<ffffffff81281f28>]  [<ffffffff81281f28>]
mlock_vma_page+0x18/0xc0
[  253.873310] RSP: 0000:ffff8804d34e99e8  EFLAGS: 00010246
[  253.873310] RAX: 006fffff8038002c RBX: ffffea00474944c0 RCX:
ffff880807636000
[  253.873310] RDX: ffffea0000000000 RSI: 00007f17a9bca000 RDI:
ffffea00474944c0
[  253.873310] RBP: ffff8804d34e99f8 R08: ffff880807020000 R09:
0000000000000000
[  253.873310] R10: 0000000000000001 R11: 0000000000002000 R12:
00007f17a9bca000
[  253.873310] R13: ffffea00474944c0 R14: 00007f17a9be0000 R15:
ffff880807020000
[  253.873310] FS:  00007f17aa31a700(0000) GS:ffff8801c9c00000(0000)
knlGS:0000000000000000
[  253.873310] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  253.873310] CR2: 00007f17a94fa000 CR3: 00000004d3b02000 CR4:
00000000000006e0
[  253.873310] DR0: 00007f17a74ca000 DR1: 0000000000000000 DR2:
0000000000000000
[  253.873310] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
0000000000000600
[  253.873310] Stack:
[  253.873310]  0000000b3de28067 ffff880b3de28e50 ffff8804d34e9aa8
ffffffff8128bc31
[  253.873310]  0000000000000301 ffffea0011850220 ffff8809a4039000
ffffea0011850238
[  253.873310]  ffff8804d34e9aa8 ffff880807636060 0000000000000001
ffff880807636348
[  253.873310] Call Trace:
[  253.873310]  [<ffffffff8128bc31>] try_to_unmap_cluster+0x1c1/0x340
[  253.873310]  [<ffffffff8128c60a>] try_to_unmap_file+0x20a/0x2e0
[  253.873310]  [<ffffffff8128c7b3>] try_to_unmap+0x73/0x90
[  253.873310]  [<ffffffff812b526d>] __unmap_and_move+0x18d/0x250
[  253.873310]  [<ffffffff812b53e9>] unmap_and_move+0xb9/0x180
[  253.873310]  [<ffffffff812b559b>] migrate_pages+0xeb/0x2f0
[  253.873310]  [<ffffffff812a0660>] ? queue_pages_pte_range+0x1a0/0x1a0
[  253.873310]  [<ffffffff812a193c>] migrate_to_node+0x9c/0xc0
[  253.873310]  [<ffffffff812a30b8>] do_migrate_pages+0x1b8/0x240
[  253.873310]  [<ffffffff812a3456>] SYSC_migrate_pages+0x316/0x380
[  253.873310]  [<ffffffff812a31ec>] ? SYSC_migrate_pages+0xac/0x380
[  253.873310]  [<ffffffff811763c6>] ? vtime_account_user+0x96/0xb0
[  253.873310]  [<ffffffff812a34ce>] SyS_migrate_pages+0xe/0x10
[  253.873310]  [<ffffffff843c4990>] tracesys+0xdd/0xe2
[  253.873310] Code: 0f 1f 00 65 48 ff 04 25 10 25 1d 00 48 83 c4 08
5b c9 c3 55 48 89 e5 53 48 83 ec 08 66 66 66 66 90 48 8b 07 48 89 fb
a8 01 75 10 <0f> 0b 66 0f 1f 44 00 00 eb fe 66 0f 1f 44 00 00 f0 0f ba
2f 15
[  253.873310] RIP  [<ffffffff81281f28>] mlock_vma_page+0x18/0xc0
[  253.873310]  RSP <ffff8804d34e99e8>
[  253.904194] ---[ end trace be59c4a7f8edab3f ]---

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Bob Liu <bob.liu@oracle.com>
---
 mm/mlock.c |    2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index d480cd6..5488d44 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -79,8 +79,6 @@ void clear_page_mlock(struct page *page)
  */
 void mlock_vma_page(struct page *page)
 {
-	BUG_ON(!PageLocked(page));
-
 	if (!TestSetPageMlocked(page)) {
 		mod_zone_page_state(page_zone(page), NR_MLOCK,
 				    hpage_nr_pages(page));
-- 
1.7.10.4

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