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

From: Sergei Trofimovich
Date: Sun Feb 24 2019 - 08:22:33 EST

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