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Subject5.0.0-rc6+: Oops at boot: RIP: 0010:__memmove+0x81/0x1a0 / vt_do_kdgkb_ioctl+0x34d/0x440 (race at reenter?)
[ 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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