Date:   Sun, 24 Feb 2019 13:22:08 +0000
From:   Sergei Trofimovich <slyfox@...ox.ru>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.com>
Subject: Re: 5.0.0-rc6+: Oops at boot: RIP: 0010:__memmove+0x81/0x1a0 /
 vt_do_kdgkb_ioctl+0x34d/0x440 (race at reenter?)

On Mon, 18 Feb 2019 09:38:10 +0100
Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:

> On Sun, Feb 17, 2019 at 11:39:57PM +0000, Sergei Trofimovich wrote:
> > [ 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?  
> 
> That could be it, care to add a lock to handle this?

Will try.

> And why does your system run loadkeys in parallel?

It comes from systemd which spawns 'systemd-vconsole-setup'
once per each vtcon at start:
    https://github.com/systemd/systemd/blob/883eb9be985fd86d9cabe967eeeab91cdd396a81/src/vconsole/90-vconsole.rules.in#L12

My system has two vtcon "devices":
  # cat /sys/devices/virtual/vtconsole/vtcon0/name
  (S) dummy device
  # cat /sys/devices/virtual/vtconsole/vtcon1/name
  (M) frame buffer device

Both trigger 'systemd-vconsole-setup' at exactly same time.

I guess multiple vtcons is i915-specific framebuffer setup:
    drivers/gpu/drm/i915/i915_drv.c:                ret = do_take_over_console(&dummy_con, 0, MAX_NR_CONSOLES - 1, 1);

This is a dmesg output with a tiny debug path applied to make
sure loadkeys is the only user of vt_do_kdgkb_ioctl() calls:

--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1996,6 +1996,14 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
        int i, j, k;
        int ret;
 
+       printk("In vt_do_kdgkb_ioctl(%d=%s)/cpu=%d/comm=%s(%d)\n",
+               cmd, (cmd == KDGKBSENT)
+                       ? "KDGKBSENT"
+                       : ((cmd == KDSKBSENT)
+                               ? "KDSKBSENT"
+                               : "UNKNOWN"),
+               hard_smp_processor_id(), current->comm, task_pid_nr(current));
+
        if (!capable(CAP_SYS_TTY_CONFIG))
                perm = 0;

Feb 24 12:06:35 sf systemd-vconsole-setup[343]: Executing "/usr/bin/loadkeys -q -C /dev/tty1 -u ru4"...
Feb 24 12:06:35 sf systemd-vconsole-setup[344]: /usr/bin/setfont succeeded.
Feb 24 12:06:35 sf systemd-vconsole-setup[344]: Executing "/usr/bin/loadkeys -q -C /dev/tty1 -u ru4"...
Feb 24 12:06:35 sf systemd-vconsole-setup[343]: Successfully forked off '(loadkeys)' as PID 423.
Feb 24 12:06:35 sf systemd-vconsole-setup[344]: Successfully forked off '(loadkeys)' as PID 424.
...
Feb 24 12:06:35 sf kernel: ^[[0;1;39m^[[0;1;39mIn vt_do_kdgkb_ioctl(19273=KDSKBSENT)/cpu=5/comm=loadkeys(424)
Feb 24 12:06:35 sf kernel: ^[[0;1;39m^[[0;1;39mIn vt_do_kdgkb_ioctl(19273=KDSKBSENT)/cpu=2/comm=loadkeys(423)
<many more of these. interleave sometimes>
...
Feb 24 12:06:35 sf systemd-vconsole-setup[343]: /usr/bin/loadkeys succeeded.
Feb 24 12:06:35 sf systemd-vconsole-setup[344]: UTF-8 kbdmode enabled on /dev/tty9
Feb 24 12:06:35 sf systemd-vconsole-setup[344]: Font and unimap successfully copied to /dev/tty9
Feb 24 12:06:35 sf systemd-vconsole-setup[343]: UTF-8 kbdmode enabled on /dev/tty9
Feb 24 12:06:35 sf systemd-vconsole-setup[343]: Font and unimap successfully copied to /dev/tty9
Feb 24 12:06:35 sf systemd-vconsole-setup[344]: UTF-8 kbdmode enabled on /dev/tty12
Feb 24 12:06:35 sf systemd-vconsole-setup[344]: Font and unimap successfully copied to /dev/tty12
Feb 24 12:06:35 sf systemd-vconsole-setup[343]: UTF-8 kbdmode enabled on /dev/tty12
Feb 24 12:06:35 sf systemd-vconsole-setup[343]: Font and unimap successfully copied to /dev/tty12

-- 

  Sergei

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