Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

[Gerald Schaefer <gerald.schaefer@de.ibm.com>]

On Mon, 15 Feb 2016 13:31:59 +0200
"Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> On Sat, Feb 13, 2016 at 12:58:31PM +0100, Sebastian Ott wrote:
> > 
> > On Sat, 13 Feb 2016, Kirill A. Shutemov wrote:
> > > Could you check if revert of fecffad25458 helps?
> > 
> > I reverted fecffad25458 on top of 721675fcf277cf - it oopsed with:
> > 
> > ¢ 1851.721062! Unable to handle kernel pointer dereference in virtual kernel address space
> > ¢ 1851.721075! failing address: 0000000000000000 TEID: 0000000000000483
> > ¢ 1851.721078! Fault in home space mode while using kernel ASCE.
> > ¢ 1851.721085! AS:0000000000d5c007 R3:00000000ffff0007 S:00000000ffffa800 P:000000000000003d
> > ¢ 1851.721128! Oops: 0004 ilc:3 ¢#1! PREEMPT SMP DEBUG_PAGEALLOC
> > ¢ 1851.721135! Modules linked in: bridge stp llc btrfs mlx4_ib mlx4_en ib_sa ib_mad vxlan xor ip6_udp_tunnel ib_core udp_tunnel ptp pps_core ib_addr ghash_s390raid6_pq prng ecb aes_s390 mlx4_core des_s390 des_generic genwqe_card sha512_s390 sha256_s390 sha1_s390 sha_common crc_itu_t dm_mod scm_block vhost_net tun vhost eadm_sch macvtap macvlan kvm autofs4
> > ¢ 1851.721183! CPU: 7 PID: 256422 Comm: bash Not tainted 4.5.0-rc3-00058-g07923d7-dirty #178
> > ¢ 1851.721186! task: 000000007fbfd290 ti: 000000008c604000 task.ti: 000000008c604000
> > ¢ 1851.721189! Krnl PSW : 0704d00180000000 000000000045d3b8 (__rb_erase_color+0x280/0x308)
> > ¢ 1851.721200!            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 EA:3
> >                Krnl GPRS: 0000000000000001 0000000000000020 0000000000000000 00000000bd07eff1
> > ¢ 1851.721205!            000000000027ca10 0000000000000000 0000000083e45898 0000000077b61198
> > ¢ 1851.721207!            000000007ce1a490 00000000bd07eff0 000000007ce1a548 000000000027ca10
> > ¢ 1851.721210!            00000000bd07c350 00000000bd07eff0 000000008c607aa8 000000008c607a68
> > ¢ 1851.721221! Krnl Code: 000000000045d3aa: e3c0d0080024       stg     %%r12,8(%%r13)
> >                           000000000045d3b0: b9040039           lgr     %%r3,%%r9
> >                          #000000000045d3b4: a53b0001           oill    %%r3,1
> >                          >000000000045d3b8: e33010000024       stg     %%r3,0(%%r1)
> >                           000000000045d3be: ec28000e007c       cgij    %%r2,0,8,45d3da
> >                           000000000045d3c4: e34020000004       lg      %%r4,0(%%r2)
> >                           000000000045d3ca: b904001c           lgr     %%r1,%%r12
> >                           000000000045d3ce: ec143f3f0056       rosbg   %%r1,%%r4,63,63,0
> > ¢ 1851.721269! Call Trace:
> > ¢ 1851.721273! (¢<0000000083e45898>! 0x83e45898)
> > ¢ 1851.721279!  ¢<000000000029342a>! unlink_anon_vmas+0x9a/0x1d8
> > ¢ 1851.721282!  ¢<0000000000283f34>! free_pgtables+0xcc/0x148
> > ¢ 1851.721285!  ¢<000000000028c376>! exit_mmap+0xd6/0x300
> > ¢ 1851.721289!  ¢<0000000000134db8>! mmput+0x90/0x118
> > ¢ 1851.721294!  ¢<00000000002d76bc>! flush_old_exec+0x5d4/0x700
> > ¢ 1851.721298!  ¢<00000000003369f4>! load_elf_binary+0x2f4/0x13e8
> > ¢ 1851.721301!  ¢<00000000002d6e4a>! search_binary_handler+0x9a/0x1f8
> > ¢ 1851.721304!  ¢<00000000002d8970>! do_execveat_common.isra.32+0x668/0x9a0
> > ¢ 1851.721307!  ¢<00000000002d8cec>! do_execve+0x44/0x58
> > ¢ 1851.721310!  ¢<00000000002d8f92>! SyS_execve+0x3a/0x48
> > ¢ 1851.721315!  ¢<00000000006fb096>! system_call+0xd6/0x258
> > ¢ 1851.721317!  ¢<000003ff997436d6>! 0x3ff997436d6
> > ¢ 1851.721319! INFO: lockdep is turned off.
> > ¢ 1851.721321! Last Breaking-Event-Address:
> > ¢ 1851.721323!  ¢<000000000045d31a>! __rb_erase_color+0x1e2/0x308
> > ¢ 1851.721327!
> > ¢ 1851.721329! ---¢ end trace 0d80041ac00cfae2 !---
> > 
> > 
> > > 
> > > And could you share how crashes looks like? I haven't seen backtraces yet.
> > > 
> > 
> > Sure. I didn't because they really looked random to me. Most of the time
> > in rcu or list debugging but I thought these have just been the messenger
> > observing a corruption first. Anyhow, here is an older one that might look
> > interesting:
> > 
> > [   59.851421] list_del corruption. next->prev should be 000000006e1eb000, but was 0000000000000400
> 
> This kinda interesting: 0x400 is TAIL_MAPPING.. Hm..
> 
> Could you check if you see the problem on commit 1c290f642101 and its
> immediate parent?
> 

How should the page->mapping poison end up as next->prev in the list of
pre-allocated THP splitting page tables? Also, commit 1c290f642101
is before the THP rework, at least the non-bisectable part, so we should
expect not to see the problem there.

0x400 is also the value of an empty pte on s390, and the thp_deposit/withdraw
listheads are placed inside the pre-allocated pagetables instead of page->lru,
because we have 2K pagetables on s390 and cannot use struct page == pgtable_t.

So, for example, two concurrent withdraws could produce such a list
corruption, because the first withdraw will overwrite the listhead at the
beginning of the pagetable with 2 empty ptes.

Has anything changed regarding the general THP deposit/withdraw logic?