Subject: Re: kernel BUG at /usr/src/kernel/lib/dynamic_debug.c:267!

From: Greg Kroah-Hartman <[email-masked]>
Date: Wed, 9 Sep 2020 20:12:51 +0200

On Wed, Sep 09, 2020 at 11:44:44AM -0600, [email-masked] wrote:
> On Wed, Sep 9, 2020 at 6:24 AM Greg Kroah-Hartman
> <[email-masked]> wrote:
> >
> > On Wed, Sep 09, 2020 at 10:00:25AM +0200, Petr Mladek wrote:
> > > On Wed 2020-09-09 14:47:45, Masami Hiramatsu wrote:
> > > > Hi Naresh,
> > > >
> > > > Thanks for reporting, it seems that you have run the kselftests/livepatch/test-livepatch.sh.
> > > > Then, I think it is better to report to Livepatch maintainers too. (I Cc'd them)
> > > >
> > > > Thank you,
> > > >
> > > > On Wed, 9 Sep 2020 10:24:09 +0530
> > > > Naresh Kamboju <[email-masked]> wrote:
> > > >
> > > > > While testing livepatch test cases on x86_64 with Linux next 20200908 tag kernel
> > > > > this kernel BUG noticed several times.
> > > > >
> > > > > metadata:
> > > > >   git branch: master
> > > > >   git repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> > > > >   git commit: dff9f829e5b0181d4ed9d35aa62d695292399b54
> > > > >   git describe: next-20200908
> > > > >     kernel-config:
> > > > > http://snapshots.linaro.org/openembedded/lkft/lkft/sumo/intel-corei7-64/lkft/linux-next/853/config
> > > > >
> > > > > kernel BUG log,
> > > > > ----------------------
> > > > > [  634.063970] % rmmod test_klp_livepatch
> > > > > [  634.114787] test_klp_atomic_replace: this has been live patched
> > > > > [  634.121953] % echo 0 > /sys/kernel/livepatch/test_klp_atomic_replace/enabled
> > > > > [  634.129391] livepatch: 'test_klp_atomic_replace': starting
> > > > > unpatching transition
> > > > > [  634.143990] livepatch: 'test_klp_atomic_replace': unpatching complete
> > > > > [  634.156223] % rmmod test_klp_atomic_replace
> > > > > [  634.235451] ------------[ cut here ]------------
> > > > > [  634.240314] kernel BUG at /usr/src/kernel/lib/dynamic_debug.c:267!
> > > > > [  634.246584] invalid opcode: 0000 [#1] SMP PTI
> > > > > [  634.250955] CPU: 0 PID: 12791 Comm: test-livepatch. Tainted: G
> > > > >   W     K   5.9.0-rc4-next-20200908 #1
> > > > > [  634.260615] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
> > > > > 2.2 05/23/2018
> > > > > [  634.268007] RIP: 0010:ddebug_exec_query+0x77b/0xb90
> > > > > [  634.272886] Code: 4c 89 ad 70 ff ff ff e9 db fb ff ff b8 03 00 00
> > > > > 00 e9 20 fb ff ff b8 02 00 00 00 e9 16 fb ff ff b8 01 00 00 00 e9 0c
> > > > > fb ff ff <0f> 0b 31 c0 e9 03 fb ff ff 49 89 f4 48 89 f7 e9 78 f9 ff ff
> > > > > 8b 15
> > > > > [  634.291630] RSP: 0018:ffff9f0c80a5bd18 EFLAGS: 00010246
> > > > > [  634.296856] RAX: 000000000000003d RBX: 0000000000000000 RCX: 0000000000000000
> > > > > [  634.303987] RDX: 000000000000003d RSI: 0000000000000000 RDI: ffff90db906583ec
> > > > > [  634.311111] RBP: ffff9f0c80a5bde8 R08: 000000000000000a R09: 000000000000003b
> > > > > [  634.318236] R10: ffff90db92610000 R11: 0000000000000246 R12: ffff90db906583ec
> > > > > [  634.325368] R13: ffffffffbe87cbc0 R14: 0000000000000000 R15: 0000000000000004
> > > > > [  634.332500] FS:  00007fd37249a740(0000) GS:ffff90dbefa00000(0000)
> > > > > knlGS:0000000000000000
> > > > > [  634.340578] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > > [  634.346315] CR2: 0000000000e6d00c CR3: 000000026a4b8004 CR4: 00000000003706f0
> > > > > [  634.353446] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > > > [  634.360570] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > > > [  634.367693] Call Trace:
> > > > > [  634.370139]  ? lock_acquire+0xa6/0x390
> > > > > [  634.373892]  ? __might_fault+0x34/0x80
> > > > > [  634.377648]  ddebug_exec_queries+0x6e/0x140
> > > > > [  634.381831]  ddebug_proc_write+0x4b/0xa0
> > > > > [  634.385756]  full_proxy_write+0x5f/0x90
> > > > > [  634.389595]  vfs_write+0xed/0x240
> > > > > [  634.392915]  ksys_write+0xad/0xf0
> > > > > [  634.396233]  ? syscall_trace_enter+0x17a/0x240
> > > > > [  634.400670]  __x64_sys_write+0x1a/0x20
> > > > > [  634.404416]  do_syscall_64+0x37/0x50
> > > > > [  634.407993]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > > > > [  634.413038] RIP: 0033:0x7fd371b84144
> > > > > [  634.416617] Code: 89 02 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00
> > > > > 00 00 00 00 66 90 48 8d 05 c1 e7 2c 00 8b 00 85 c0 75 13 b8 01 00 00
> > > > > 00 0f 05 <48> 3d 00 f0 ff ff 77 54 c3 0f 1f 00 41 54 49 89 d4 55 48 89
> > > > > f5 53
> > > > > [  634.435362] RSP: 002b:00007ffd19447658 EFLAGS: 00000246 ORIG_RAX:
> > > > > 0000000000000001
> > > > > [  634.442928] RAX: ffffffffffffffda RBX: 00000000000000bc RCX: 00007fd371b84144
> > > > > [  634.450059] RDX: 00000000000000bc RSI: 0000000000e6cf70 RDI: 0000000000000001
> > > > > [  634.457181] RBP: 0000000000e6cf70 R08: 00000000000000e9 R09: 0000000000000000
> > > > > [  634.464305] R10: 00007ffd19447c48 R11: 0000000000000246 R12: 00007fd371e4e760
> > > > > [  634.471429] R13: 00000000000000bc R14: 00007fd371e49760 R15: 00000000000000bc
> > > > > [  634.478559] Modules linked in: trace_printk sch_fq 8021q
> > > > > iptable_filter xt_mark ip_tables cls_bpf sch_ingress veth algif_hash
> > > > > x86_pkg_temp_thermal fuse [last unloaded: test_klp_atomic_replace]
> > > > > [  634.495695] ---[ end trace d04d7e11bd1458bf ]---
> > > > > [  634.500333] RIP: 0010:ddebug_exec_query+0x77b/0xb90
> > > > > [  634.505218] Code: 4c 89 ad 70 ff ff ff e9 db fb ff ff b8 03 00 00
> > > > > 00 e9 20 fb ff ff b8 02 00 00 00 e9 16 fb ff ff b8 01 00 00 00 e9 0c
> > > > > fb ff ff <0f> 0b 31 c0 e9 03 fb ff ff 49 89 f4 48 89 f7 e9 78 f9 ff ff
> > > > > 8b 15
> > > > > [  634.523969] RSP: 0018:ffff9f0c80a5bd18 EFLAGS: 00010246
> > > > > [  634.529197] RAX: 000000000000003d RBX: 0000000000000000 RCX: 0000000000000000
> > > > > [  634.536330] RDX: 000000000000003d RSI: 0000000000000000 RDI: ffff90db906583ec
> > > > > [  634.543462] RBP: ffff9f0c80a5bde8 R08: 000000000000000a R09: 000000000000003b
> > > > > [  634.550593] R10: ffff90db92610000 R11: 0000000000000246 R12: ffff90db906583ec
> > > > > [  634.557727] R13: ffffffffbe87cbc0 R14: 0000000000000000 R15: 0000000000000004
> > > > > [  634.564869] FS:  00007fd37249a740(0000) GS:ffff90dbefa00000(0000)
> > > > > knlGS:0000000000000000
> > > > > [  634.572953] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > > [  634.578699] CR2: 0000000000e6d00c CR3: 000000026a4b8004 CR4: 00000000003706f0
> > > > > [  634.585829] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > > > [  634.592964] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > >
> > > It is caused by the commit 42f07816ac0cc79792811 ("dyndbg:
> > > fix problem parsing format="foo bar"). It modified the condition
> > > when the above BUG() gets triggered.
> > >
> > > It has even been reported by the kernel test robot, see
> > > https://lore.kernel.org/lkml/20200902074124.GP4299@shao2-debian/
> > >
> > >
> > > It is triggered when the livepatching selftest is trying to restore the
> > > original setting of dynamic debug messages in the livepatch framework.
> > >
> > > It can get reliably reproduced by the following call:
> > >
> > > $> echo -n 'file kernel/livepatch/transition.c line 586 =_' > \
> > >    /sys/kernel/debug/dynamic_debug/control
> > >
> > >
> > > Adding people from the problematic patch into CC.
> > >
> > > I haven't dived into the dynamic debug code yet. The logic might
> > > be wrong.
> > >
> > > Anyway, the BUG_ON() should get replaced by a normal error message.
> > > There is no reason to panic() when a string can't be parsed !!!
> >
> > The above mentioned patch was trying to fix things so that the BUG_ON()
> > would not be hit, I guess that's not really happening here :(
> >
> > Jim, can you look into this?
> >
> > thanks,
> >
> > greg k-h
> 
> Ive been down with a stomach bug for past week,
> Im feeling normal-ish now, but playing catchup, and taking some NMIs.
> 
> 
>  commit 42f07816ac0cc79792811 ("dyndbg: fix problem parsing format="foo bar").
> 
> I'm miffed and embarrassed that the quick fix also broke.
> Im not experienced enough to know what "normal" handling looks like
> for reactive breakages like this...
> 
> If you want to revert the 2 commits (original feature + fixup),
> Id find some stress relief in that, and would take a clean run at it later.
> 
> I hope to steal a few hrs from the catchup tasks to investigate this RSN.
> 
> thanks and apologies

No worries, go rest and get better, that's more important than this
little stuff.

I'll go revert both patches from my tree in the morning, which should
clear these issues up.

thanks,

greg k-h