5.0.0-rc6+: Oops at boot: RIP: 0010:__memmove+0x81/0x1a0 / vt_do_kdgkb_ioctl+0x34d/0x440 (race at reenter?)

[Sergei Trofimovich <slyfox@inbox.ru>]

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[ Copying as is from https://bugzilla.kernel.org/show_bug.cgi?id=202605
  and sending to LKML. Greg, Jiri, can you clarify mailing
  list im  MAINTAINERS as well?
      https://github.com/torvalds/linux/blob/master/MAINTAINERS#L15527
  mentions no list for tty/vt/. ]

Kernel Oops
  [   38.739241] Oops: 0003 [#1] PREEMPT SMP
  [   38.739243] CPU: 6 PID: 388 Comm: loadkeys Tainted: G         C        5.0.0-rc6-00153-g5ded5871030e #91
  [   38.739244] Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./H77M-D3H, BIOS F12 11/14/2013
  [   38.739249] RIP: 0010:__memmove+0x81/0x1a0
happes on a fresh vanilla master kernel roughly at boot
(before tty login prompt):
  $ uname -r
  5.0.0-rc6-00153-g5ded5871030e

The kernel page fault happens at 'loadkeys start'.
I suspect some kind of race at reenter of vt_do_kdgkb_ioctl(KDSKBSENT):
    https://github.com/torvalds/linux/blob/master/drivers/tty/vt/keyboard.c#L1986

The oops trace looks similar to the following reports (no details besides Oops)
    https://bugzilla.kernel.org/show_bug.cgi?id=194589
    https://bugzilla.kernel.org/show_bug.cgi?id=202111

[   38.044921] IPv6: ADDRCONF(NETDEV_CHANGE): br0: link becomes ready
[   38.533196] usb 1-1.2: r8712u: CustomerID = 0x0000
[   38.533200] usb 1-1.2: r8712u: MAC Address from efuse = 00:0d:81:a9:09:90
[   38.533203] usb 1-1.2: r8712u: Loading firmware from "rtlwifi/rtl8712u.bin"
[   38.533331] usbcore: registered new interface driver r8712u
[   38.736178] BUG: unable to handle kernel paging request at ffff9c8735448000
[   38.737215] #PF error: [PROT] [WRITE]
[   38.737216] PGD 288a05067 P4D 288a05067 PUD 288a07067 PMD 7f60c2063 PTE 80000007f5448161
[   38.739241] Oops: 0003 [#1] PREEMPT SMP
[   38.739243] CPU: 6 PID: 388 Comm: loadkeys Tainted: G         C        5.0.0-rc6-00153-g5ded5871030e #91
[   38.739244] Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./H77M-D3H, BIOS F12 11/14/2013
[   38.739249] RIP: 0010:__memmove+0x81/0x1a0
[   38.739251] Code: 4c 89 4f 10 4c 89 47 18 48 8d 7f 20 73 d4 48 83 c2 20 e9 a2 00 00 00 66 90 48 89 d1 4c 8b 5c 16 f8 4c 8d 54 17 f8 48 c1 e9 03 <f3> 48 a5 4d 89 1a e9 0c 01 00 00 0f 1f 40 00 48 89 d1 4c 8b 1e 49
[   38.739252] RSP: 0018:ffffa1b9002d7d08 EFLAGS: 00010203
[   38.745857] RAX: ffff9c873541af43 RBX: ffff9c873541af43 RCX: 00000c6f105cd6bf
[   38.745858] RDX: 0000637882e986b6 RSI: ffff9c8735447ffb RDI: ffff9c8735447ffb
[   38.745859] RBP: ffff9c8739cd3800 R08: ffff9c873b802f00 R09: 00000000fffff73b
[   38.745860] R10: ffffffffb82b35f1 R11: 00505b1b004d5b1b R12: 0000000000000000
[   38.745861] R13: ffff9c873541af3d R14: 000000000000000b R15: 000000000000000c
[   38.745862] FS:  00007f450c390580(0000) GS:ffff9c873f180000(0000) knlGS:0000000000000000
[   38.745863] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   38.745864] CR2: ffff9c8735448000 CR3: 00000007e213c002 CR4: 00000000000606e0
[   38.745865] Call Trace:
[   38.745871]  vt_do_kdgkb_ioctl+0x34d/0x440
[   38.745875]  vt_ioctl+0xba3/0x1190
[   38.745879]  ? __bpf_prog_run32+0x39/0x60
[   38.745882]  ? mem_cgroup_commit_charge+0x7b/0x4e0
[   38.762583]  tty_ioctl+0x23f/0x920
[   38.762586]  ? preempt_count_sub+0x98/0xe0
[   38.762590]  ? __seccomp_filter+0x67/0x600
[   38.762594]  do_vfs_ioctl+0xa2/0x6a0
[   38.762597]  ? syscall_trace_enter+0x192/0x2d0
[   38.762599]  ksys_ioctl+0x3a/0x70
[   38.762601]  __x64_sys_ioctl+0x16/0x20
[   38.762604]  do_syscall_64+0x54/0xe0
[   38.772513]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   38.772515] RIP: 0033:0x7f450c2bb427
[   38.772517] Code: 00 00 00 75 0c 48 c7 c0 ff ff ff ff 48 83 c4 18 c3 e8 8d d2 01 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 39 da 0c 00 f7 d8 64 89 01 48
[   38.772518] RSP: 002b:00007fffbcedd348 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[   38.772519] RAX: ffffffffffffffda RBX: 000000000000000b RCX: 00007f450c2bb427
[   38.772520] RDX: 00007fffbcedd360 RSI: 0000000000004b49 RDI: 0000000000000003
[   38.772521] RBP: 00007fffbcedd361 R08: 00007f450c389c40 R09: 000055cbef2494a0
[   38.772522] R10: 0000000000000000 R11: 0000000000000246 R12: 000055cbef2412b0
[   38.772522] R13: 00007fffbcedd360 R14: 000000000000000b R15: 0000000000000003
[   38.772525] Modules linked in: snd_hda_codec_hdmi bridge r8712u(C) stp llc snd_hda_codec_via snd_hda_codec_generic snd_hda_intel snd_hda_codec x86_pkg_temp_thermal dummy kvm_intel snd_hwdep snd_hda_core snd_pcm snd_timer kvm snd atl1c soundcore irqbypass xfs tun nf_conntrack_ftp nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 loop fuse binfmt_misc ipv6
[   38.779196] r8712u 1-1.2:1.0 wl0: renamed from wlan0
[   38.779240] CR2: ffff9c8735448000
[   38.790894] ---[ end trace 8116e48ba19076a0 ]---
[   38.790897] RIP: 0010:__memmove+0x81/0x1a0
[   38.790898] Code: 4c 89 4f 10 4c 89 47 18 48 8d 7f 20 73 d4 48 83 c2 20 e9 a2 00 00 00 66 90 48 89 d1 4c 8b 5c 16 f8 4c 8d 54 17 f8 48 c1 e9 03 <f3> 48 a5 4d 89 1a e9 0c 01 00 00 0f 1f 40 00 48 89 d1 4c 8b 1e 49
[   38.790899] RSP: 0018:ffffa1b9002d7d08 EFLAGS: 00010203
[   38.790900] RAX: ffff9c873541af43 RBX: ffff9c873541af43 RCX: 00000c6f105cd6bf
[   38.790901] RDX: 0000637882e986b6 RSI: ffff9c8735447ffb RDI: ffff9c8735447ffb
[   38.790902] RBP: ffff9c8739cd3800 R08: ffff9c873b802f00 R09: 00000000fffff73b
[   38.790903] R10: ffffffffb82b35f1 R11: 00505b1b004d5b1b R12: 0000000000000000
[   38.790904] R13: ffff9c873541af3d R14: 000000000000000b R15: 000000000000000c
[   38.790905] FS:  00007f450c390580(0000) GS:ffff9c873f180000(0000) knlGS:0000000000000000
[   38.790906] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   38.790907] CR2: ffff9c8735448000 CR3: 00000007e213c002 CR4: 00000000000606e0
[   38.790908] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:34
[   38.790909] in_atomic(): 0, irqs_disabled(): 1, pid: 388, name: loadkeys
[   38.790911] CPU: 6 PID: 388 Comm: loadkeys Tainted: G      D  C        5.0.0-rc6-00153-g5ded5871030e #91
[   38.790911] Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./H77M-D3H, BIOS F12 11/14/2013
[   38.790912] Call Trace:
[   38.790917]  dump_stack+0x67/0x90
[   38.822550]  ? wake_up_klogd+0x10/0x70
[   38.822553]  ___might_sleep.cold.17+0xd4/0xe4
[   38.822556]  exit_signals+0x1c/0x200
[   38.822558]  do_exit+0xa8/0xb90
[   38.822560]  ? ksys_ioctl+0x3a/0x70
[   38.822562]  rewind_stack_do_exit+0x17/0x20

I suspect my system runs multiple loadkeys instances in parallel
and that triggers an Oops.

I noticed that vt_do_kdgkb_ioctl() uses global variable to optimise
func_table re-allocation. Even comment hints at lack of locking:

    /* FIXME: This one needs untangling and locking */
    int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)

    https://github.com/torvalds/linux/blob/master/drivers/tty/vt/keyboard.c#L2084

Could that be it?

func_table[] is a global array pointers to to initially statically and later
dynamically allocated buffer.
    https://github.com/torvalds/linux/blob/master/drivers/tty/vt/defkeymap.c_shipped#L191

Thanks!

-- 

  Sergei

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