[SRU][Trusty/Utopic][PATCH 1/1] mm/balloon_compaction: Fix Regression of LP#1572562

[Gavin Guo]

BugLink: http://bugs.launchpad.net/bugs/1598197

Fix the nested spinlock() in balloon_page_dequeue() which would cause
the deadlock and the following coredump while deflating the balloon:

[  106.604006] NMI backtrace for cpu 0
[  106.604006] CPU: 0 PID: 231 Comm: vballoon Not tainted 3.13.0-91-generic #138-Ubuntu
[  106.604006] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[  106.604006] task: ffff8801353d4800 ti: ffff880134c20000 task.ti: ffff880134c20000
[  106.604006] RIP: 0010:[<ffffffff817319b7>]  [<ffffffff817319b7>] _raw_spin_lock_irqsave+0x47/0x60
[  106.604006] RSP: 0018:ffff880134c21dc8  EFLAGS: 00000002
[  106.604006] RAX: 000000000000025e RBX: ffffea00014323c0 RCX: 0000000000005ee2
[  106.604006] RDX: 0000000000005ee0 RSI: 0000000000005ee2 RDI: ffff880138e649d8
[  106.604006] RBP: ffff880134c21dc8 R08: 0000000000000002 R09: 000000000000002f
[  106.604006] R10: 0000000000000004 R11: 0000000000000005 R12: ffff880138e649d8
[  106.604006] R13: ffff880138e649c0 R14: ffffea0001432380 R15: 0000000000000206
[  106.604006] FS:  0000000000000000(0000) GS:ffff88013b200000(0000) knlGS:0000000000000000
[  106.604006] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  106.604006] CR2: 0000000001a94a58 CR3: 00000000a9d59000 CR4: 00000000000006f0
[  106.604006] Stack:
[  106.604006]  ffff880134c21e00 ffffffff81176748 ffff88013536b800 0000000000000100
[  106.604006]  ffff880138e649c0 0000000000000000 ffff88013536b820 ffff880134c21e40
[  106.604006]  ffffffff8143539f ffff88013536b868 ffff88013536b800 fffffffffff7d090
[  106.604006] Call Trace:
[  106.604006]  [<ffffffff81176748>] balloon_page_dequeue+0x78/0x140
[  106.604006]  [<ffffffff8143539f>] leak_balloon+0x7f/0x110
[  106.604006]  [<ffffffff81435776>] balloon+0x166/0x2a0
[  106.604006]  [<ffffffff810adad0>] ? prepare_to_wait_event+0x100/0x100
[  106.604006]  [<ffffffff81435610>] ? update_balloon_stats+0xf0/0xf0
[  106.604006]  [<ffffffff8108dc79>] kthread+0xc9/0xe0
[  106.604006]  [<ffffffff8108dbb0>] ? kthread_create_on_node+0x1c0/0x1c0
[  106.604006]  [<ffffffff8173a3e8>] ret_from_fork+0x58/0x90
[  106.604006]  [<ffffffff8108dbb0>] ? kthread_create_on_node+0x1c0/0x1c0

Signed-off-by: Gavin Guo <gavin.guo at canonical.com>
---
 mm/balloon_compaction.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 65f9c733bc2d..bd60eebda2f4 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -101,9 +101,7 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
 				continue;
 			}
 #endif
-			spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 			balloon_page_delete(page);
-			spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 			unlock_page(page);
 			dequeued_page = true;
 			break;
-- 
2.7.4