[PATCH] mm: memcontrol: per-lruvec stats infrastructure fix

[Johannes Weiner]

Fix the following crash in the new cgroup stat keeping code:

Freeing unused kernel memory: 856K
Write protecting the kernel read-only data: 8192k
Freeing unused kernel memory: 1104K
Freeing unused kernel memory: 588K
page:ffffea000005d8c0 count:2 mapcount:1 mapping:          (null) index:0x0
flags: 0x800000000000801(locked|reserved)
raw: 0800000000000801 0000000000000000 0000000000000000 0000000200000000
raw: ffffea000005d8e0 ffffea000005d8e0 0000000000000000 0000000000000000
page dumped because: not cgrouped, will crash
BUG: unable to handle kernel NULL pointer dereference at 00000000000004d8
IP: page_add_file_rmap+0x56/0xf0
PGD 0
P4D 0
Oops: 0000 [#1] SMP
CPU: 0 PID: 1 Comm: init Not tainted 4.12.0-rc2-00065-g390160f076be-dirty #326
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-20170228_101828-anatol 04/01/2014
task: ffff88007d380000 task.stack: ffffc9000031c000
RIP: 0010:page_add_file_rmap+0x56/0xf0
RSP: 0000:ffffc9000031fd88 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffffea000005d8c0 RCX: 0000000000000006
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88007ffde000
RBP: ffffc9000031fd98 R08: 0000000000000003 R09: 0000000000000000
R10: ffffc9000031fd18 R11: 0000000000000000 R12: ffff88007ffdfab8
R13: ffffea000005d8c0 R14: ffff88007c76d508 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000004d8 CR3: 000000007c76c000 CR4: 00000000000006b0
Call Trace:
 alloc_set_pte+0xb5/0x2f0
 finish_fault+0x2b/0x50
 __handle_mm_fault+0x3e5/0xb90
 handle_mm_fault+0x284/0x340
 __do_page_fault+0x1fb/0x410
 do_page_fault+0xc/0x10
 page_fault+0x22/0x30

This is a special page being faulted, and these will never be charged
to a cgroup. Assume the root cgroup for uncharged pages to fix this.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
 include/linux/memcontrol.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index a282eb2a6cc3..bea6f08e9e16 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -585,18 +585,26 @@ static inline void mod_lruvec_state(struct lruvec *lruvec,
 static inline void __mod_lruvec_page_state(struct page *page,
 					   enum node_stat_item idx, int val)
 {
+	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 
-	lruvec = mem_cgroup_lruvec(page_pgdat(page), page->mem_cgroup);
+	/* Special pages in the VM aren't charged, use root */
+	memcg = page->mem_cgroup ? : root_mem_cgroup;
+
+	lruvec = mem_cgroup_lruvec(page_pgdat(page), memcg);
 	__mod_lruvec_state(lruvec, idx, val);
 }
 
 static inline void mod_lruvec_page_state(struct page *page,
 					 enum node_stat_item idx, int val)
 {
+	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 
-	lruvec = mem_cgroup_lruvec(page_pgdat(page), page->mem_cgroup);
+	/* Special pages in the VM aren't charged, use root */
+	memcg = page->mem_cgroup ? : root_mem_cgroup;
+
+	lruvec = mem_cgroup_lruvec(page_pgdat(page), memcg);
 	mod_lruvec_state(lruvec, idx, val);
 }
 
-- 
2.13.0