Re: [Resend PATCH 1/6] mm/memcg: warning on !memcg after readahead page charged

[Michal Hocko]

On Thu 20-08-20 10:58:51, Qian Cai wrote:
> On Tue, Aug 11, 2020 at 07:10:27PM +0800, Alex Shi wrote:
> > Since readahead page is charged on memcg too, in theory we don't have to
> > check this exception now. Before safely remove them all, add a warning
> > for the unexpected !memcg.
> > 
> > Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> 
> This will trigger,

Thanks for the report!
 
> [ 1863.916499] LTP: starting move_pages12
> [ 1863.946520] page:000000008ccc1062 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1fd3c0
> [ 1863.946553] head:000000008ccc1062 order:5 compound_mapcount:0 compound_pincount:0

Hmm, this is really unexpected. How did we get order-5 page here? Is
this some special mappaing that sys_move_pages should just ignore?

> [ 1863.946568] anon flags: 0x7fff800001000d(locked|uptodate|dirty|head)
> [ 1863.946584] raw: 007fff800001000d c000000016ebfcd8 c000000016ebfcd8 c000001feaf46d59
> [ 1863.946609] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
> [ 1863.946632] page dumped because: VM_WARN_ON_ONCE_PAGE(!memcg)
> [ 1863.946669] ------------[ cut here ]------------
> [ 1863.946694] WARNING: CPU: 16 PID: 35307 at mm/memcontrol.c:6908 mem_cgroup_migrate+0x5f8/0x610
> [ 1863.946708] Modules linked in: vfio_pci vfio_virqfd vfio_iommu_spapr_tce vfio vfio_spapr_eeh loop kvm_hv kvm ip_tables x_tables sd_mod bnx2x tg3 ahci libahci libphy mdio firmware_class libata dm_mirror dm_region_hash dm_log dm_mod
> [ 1863.946801] CPU: 16 PID: 35307 Comm: move_pages12 Not tainted 5.9.0-rc1-next-20200820 #4
> [ 1863.946834] NIP:  c0000000003fcb48 LR: c0000000003fcb38 CTR: 0000000000000000
> [ 1863.946856] REGS: c000000016ebf6f0 TRAP: 0700   Not tainted  (5.9.0-rc1-next-20200820)
> [ 1863.946879] MSR:  900000000282b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 28242882  XER: 00000000
> [ 1863.946915] CFAR: c00000000032c644 IRQMASK: 0 
>                GPR00: c0000000003fcb38 c000000016ebf980 c000000005923200 0000000000000031 
>                GPR04: 0000000000000000 0000000000000000 0000000000000027 c000001ffd727190 
>                GPR08: 0000000000000023 0000000000000001 c0000000058f3200 0000000000000001 
>                GPR12: 0000000000002000 c000001ffffe3800 c000000000b26a68 0000000000000000 
>                GPR16: c000000016ebfc20 c000000016ebfcd8 0000000000000020 0000000000000001 
>                GPR20: c00c00080724f000 c0000000003c8770 0000000000000000 c000000016ebfcd0 
>                GPR24: 0000000000000000 fffffffffffffff5 0000000000000002 0000000000000000 
>                GPR28: 0000000000000000 0000000000000001 0000000000000000 c00c000007f4f000 
> [ 1863.947142] NIP [c0000000003fcb48] mem_cgroup_migrate+0x5f8/0x610
> [ 1863.947164] LR [c0000000003fcb38] mem_cgroup_migrate+0x5e8/0x610
> [ 1863.947185] Call Trace:
> [ 1863.947203] [c000000016ebf980] [c0000000003fcb38] mem_cgroup_migrate+0x5e8/0x610 (unreliable)
> [ 1863.947241] [c000000016ebf9c0] [c0000000003c9080] migrate_page_states+0x4e0/0xce0
> [ 1863.947274] [c000000016ebf9f0] [c0000000003cbbec] migrate_page+0x8c/0x120
> [ 1863.947307] [c000000016ebfa30] [c0000000003ccf10] move_to_new_page+0x190/0x670
> [ 1863.947341] [c000000016ebfaf0] [c0000000003ced08] migrate_pages+0xfb8/0x1880
> [ 1863.947365] [c000000016ebfc00] [c0000000003cf670] move_pages_and_store_status.isra.45+0xa0/0x160
> [ 1863.947399] [c000000016ebfc80] [c0000000003cfef4] sys_move_pages+0x7c4/0xed0
> [ 1863.947434] [c000000016ebfdc0] [c00000000002c678] system_call_exception+0xf8/0x1d0
> [ 1863.947459] [c000000016ebfe20] [c00000000000d0a8] system_call_common+0xe8/0x218
> [ 1863.947481] Instruction dump:
> [ 1863.947502] 7fc3f378 4bfee82d 7c0802a6 3c82fb20 7fe3fb78 38844fc8 f8010050 4bf2fad5 
> [ 1863.947527] 60000000 39200001 3d42fffd 992a82fb <0fe00000> e8010050 eb810020 7c0803a6 
> [ 1863.947563] CPU: 16 PID: 35307 Comm: move_pages12 Not tainted 5.9.0-rc1-next-20200820 #4
> [ 1863.947594] Call Trace:
> [ 1863.947615] [c000000016ebf4d0] [c0000000006f6008] dump_stack+0xfc/0x174 (unreliable)
> [ 1863.947642] [c000000016ebf520] [c0000000000c9004] __warn+0xc4/0x14c
> [ 1863.947665] [c000000016ebf5b0] [c0000000006f4b68] report_bug+0x108/0x1f0
> [ 1863.947689] [c000000016ebf650] [c0000000000234f4] program_check_exception+0x104/0x2e0
> [ 1863.947724] [c000000016ebf680] [c000000000009664] program_check_common_virt+0x2c4/0x310
> [ 1863.947751] --- interrupt: 700 at mem_cgroup_migrate+0x5f8/0x610
>                    LR = mem_cgroup_migrate+0x5e8/0x610
> [ 1863.947786] [c000000016ebf9c0] [c0000000003c9080] migrate_page_states+0x4e0/0xce0
> [ 1863.947810] [c000000016ebf9f0] [c0000000003cbbec] migrate_page+0x8c/0x120
> [ 1863.947843] [c000000016ebfa30] [c0000000003ccf10] move_to_new_page+0x190/0x670
> [ 1863.947867] [c000000016ebfaf0] [c0000000003ced08] migrate_pages+0xfb8/0x1880
> [ 1863.947901] [c000000016ebfc00] [c0000000003cf670] move_pages_and_store_status.isra.45+0xa0/0x160
> [ 1863.947936] [c000000016ebfc80] [c0000000003cfef4] sys_move_pages+0x7c4/0xed0
> [ 1863.947969] [c000000016ebfdc0] [c00000000002c678] system_call_exception+0xf8/0x1d0
> [ 1863.948002] [c000000016ebfe20] [c00000000000d0a8] system_call_common+0xe8/0x218
> [ 1863.948034] irq event stamp: 410
> [ 1863.948054] hardirqs last  enabled at (409): [<c000000000184564>] console_unlock+0x6b4/0x990
> [ 1863.948092] hardirqs last disabled at (410): [<c00000000000965c>] program_check_common_virt+0x2bc/0x310
> [ 1863.948126] softirqs last  enabled at (0): [<c0000000000c59a8>] copy_process+0x788/0x1950
> [ 1863.948229] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [ 1863.948316] ---[ end trace 74f8f4df751b0259 ]---
-- 
Michal Hocko
SUSE Labs