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Subject[PATCH 1/4] memcg: fix mem_cgroup_get_reclaim_stat_from_page
In case of swapin, a new page is added to lru before it is charged,
so page->pc->mem_cgroup points to NULL or last mem_cgroup the page
was charged before.

In the latter case, if the mem_cgroup has already freed by rmdir,
the area pointed to by page->pc->mem_cgroup may have invalid data.

Actually, I saw general protection fault.

general protection fault: 0000 [#1] SMP
last sysfs file: /sys/devices/system/cpu/cpu15/cache/index1/shared_cpu_map
CPU 4
Modules linked in: ipt_REJECT xt_tcpudp iptable_filter ip_tables x_tables bridge stp ipv6 autofs4 hidp rfcomm l2cap bluetooth sunrpc dm_mirror dm_region_hash dm_log dm_multipath dm_mod rfkill input_polldev sbs sbshc battery ac lp sg ide_cd_mod cdrom button serio_raw acpi_memhotplug parport_pc e1000 rtc_cmos parport rtc_core rtc_lib i2c_i801 i2c_core shpchp pcspkr ata_piix libata megaraid_mbox megaraid_mm sd_mod scsi_mod ext3 jbd ehci_hcd ohci_hcd uhci_hcd [last unloaded: microcode]
Pid: 26038, comm: page01 Tainted: G W 2.6.28-rc9-mm1-mmotm-2008-12-22-16-14-f2ab3dea #1
RIP: 0010:[<ffffffff8028e710>] [<ffffffff8028e710>] update_page_reclaim_stat+0x2f/0x42
RSP: 0000:ffff8801ee457da8 EFLAGS: 00010002
RAX: 32353438312021c8 RBX: 0000000000000000 RCX: 32353438312021c8
RDX: 0000000000000000 RSI: ffff8800cb0b1000 RDI: ffff8801164d1d28
RBP: ffff880110002cb8 R08: ffff88010f2eae23 R09: 0000000000000001
R10: ffff8800bc514b00 R11: ffff880110002c00 R12: 0000000000000000
R13: ffff88000f484100 R14: 0000000000000003 R15: 00000000001200d2
FS: 00007f8a261726f0(0000) GS:ffff88010f2eaa80(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007f8a25d22000 CR3: 00000001ef18c000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process page01 (pid: 26038, threadinfo ffff8801ee456000, task ffff8800b585b960)
Stack:
ffffe200071ee568 ffff880110001f00 0000000000000000 ffffffff8028ea17
ffff88000f484100 0000000000000000 0000000000000020 00007f8a25d22000
ffff8800bc514b00 ffffffff8028ec34 0000000000000000 0000000000016fd8
Call Trace:
[<ffffffff8028ea17>] ? ____pagevec_lru_add+0xc1/0x13c
[<ffffffff8028ec34>] ? drain_cpu_pagevecs+0x36/0x89
[<ffffffff802a4f8c>] ? swapin_readahead+0x78/0x98
[<ffffffff8029a37a>] ? handle_mm_fault+0x3d9/0x741
[<ffffffff804da654>] ? do_page_fault+0x3ce/0x78c
[<ffffffff804d7a42>] ? trace_hardirqs_off_thunk+0x3a/0x3c
[<ffffffff804d860f>] ? page_fault+0x1f/0x30
Code: cc 55 48 8d af b8 0d 00 00 48 89 f7 53 89 d3 e8 39 85 02 00 48 63 d3 48 ff 44 d5 10 45 85 e4 74 05 48 ff 44 d5 00 48 85 c0 74 0e <48> ff 44 d0 10 45 85 e4 74 04 48 ff 04 d0 5b 5d 41 5c c3 41 54
RIP [<ffffffff8028e710>] update_page_reclaim_stat+0x2f/0x42
RSP <ffff8801ee457da8>
ChangeLog: RFC->v1
- add comments to smp_rmb.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 17 ++++++++++++++++-
1 files changed, 16 insertions(+), 1 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e2996b8..b665127 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -358,6 +358,10 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
return;

pc = lookup_page_cgroup(page);
+ /*
+ * Used bit is set without atomic ops but after smp_wmb().
+ * For making pc->mem_cgroup visible, insert smp_rmb() here.
+ */
smp_rmb();
/* unused page is not rotated. */
if (!PageCgroupUsed(pc))
@@ -374,7 +378,10 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
if (mem_cgroup_disabled())
return;
pc = lookup_page_cgroup(page);
- /* barrier to sync with "charge" */
+ /*
+ * Used bit is set without atomic ops but after smp_wmb().
+ * For making pc->mem_cgroup visible, insert smp_rmb() here.
+ */
smp_rmb();
if (!PageCgroupUsed(pc))
return;
@@ -559,6 +566,14 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
return NULL;

pc = lookup_page_cgroup(page);
+ /*
+ * Used bit is set without atomic ops but after smp_wmb().
+ * For making pc->mem_cgroup visible, insert smp_rmb() here.
+ */
+ smp_rmb();
+ if (!PageCgroupUsed(pc))
+ return NULL;
+
mz = page_cgroup_zoneinfo(pc);
if (!mz)
return NULL;

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