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Date:   Wed, 3 Aug 2022 21:55:18 -0700
From:   Josh Poimboeuf <jpoimboe@kernel.org>
To:     Chen Zhongjin <chenzhongjin@huawei.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        linux-arch@vger.kernel.org, peterz@infradead.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com, mbenes@suse.cz
Subject: Re: [PATCH] Revert "x86/unwind/orc: Don't skip the first frame for
 inactive tasks"
Message-ID: <20220804045518.bfhe3rxhpkxzn4hk@treble>
References: <20220727031506.59322-1-chenzhongjin@huawei.com>
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On Wed, Jul 27, 2022 at 11:15:06AM +0800, Chen Zhongjin wrote:
> This reverts commit f1d9a2abff66aa8156fbc1493abed468db63ea48.
> 
> When CONFIG_GCOV_PROFILE_ALL is enabled, show_stack() and related
> functions (e.g. dump_stack) will break for x86 ORC unwinder.
> 
> Call Trace:
>  <TASK>
>  ? dump_stack_lvl+0x83/0xb7
>  ? schedule+0x1/0x190
>  ? dump_stack+0x13/0x1f
>  ? handler_pre0+0x3f/0x53 [kp_unwind]
>  ...
> 
> show_trace_log_lvl() searches text address on stack to validate
> whether unwind results are reliable. The code:

Hi,

Thanks for the patch.  The change itself makes sense, though I'm having
trouble recreating the bug described in the patch description.

I enabled CONFIG_GCOV_PROFILE_ALL and did 'echo l >
/proc/sysrq-trigger', but I got a valid stack trace:

  # echo l > /proc/sysrq-trigger
  [  343.916728] sysrq: Show backtrace of all active CPUs
  [  343.917459] NMI backtrace for cpu 2
  [  343.917884] CPU: 2 PID: 1007 Comm: bash Not tainted 5.19.0-rc8+ #68
  [  343.918562] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-1.fc36 04/01/2014
  [  343.919534] Call Trace:
  [  343.919904]  <TASK>
  [  343.920226]  dump_stack_lvl+0xcc/0x11b
  [  343.920742]  dump_stack+0x17/0x24
  [  343.921199]  nmi_cpu_backtrace.cold+0xb5/0x10d
  [  343.921795]  ? lapic_can_unplug_cpu+0xa0/0xa0
  [  343.922375]  nmi_trigger_cpumask_backtrace+0x171/0x200
  [  343.923053]  arch_trigger_cpumask_backtrace+0x21/0x30
  [  343.923599]  sysrq_handle_showallcpus+0x1f/0x30
  [  343.924104]  __handle_sysrq.cold+0x81/0x234
  [  343.924576]  write_sysrq_trigger+0x6a/0x90
  [  343.925098]  proc_reg_write+0x99/0x120
  [  343.925587]  vfs_write+0x16c/0x350
  [  343.926093]  ksys_write+0x8c/0x180
  [  343.926597]  __x64_sys_write+0x21/0x30
  [  343.927144]  do_syscall_64+0x76/0x100
  [  343.927676]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
  [  343.928343] RIP: 0033:0x7f555e8f7b50
  [  343.928822] Code: 73 01 c3 48 8b 0d 38 83 2c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 79 db 2c 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 1e e3 01 00 48 89 04 24
  [  343.930801] RSP: 002b:00007ffdd20d0978 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
  [  343.931761] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f555e8f7b50
  [  343.932551] RDX: 0000000000000002 RSI: 000055ff471bfe20 RDI: 0000000000000001
  [  343.933347] RBP: 000055ff471bfe20 R08: 00007f555ebc2740 R09: 00007f555f80f700
  [  343.934155] R10: 0000000000000073 R11: 0000000000000246 R12: 0000000000000002
  [  343.934962] R13: 0000000000000001 R14: 00007f555ebc15e0 R15: 00007f555ebbd3c0
  [  343.935798]  </TASK>
  [  343.936341] Sending NMI from CPU 2 to CPUs 0-1,3:
  [  343.937163] NMI backtrace for cpu 3
  [  343.937167] CPU: 3 PID: 600 Comm: systemd-journal Not tainted 5.19.0-rc8+ #68

Was this with an upstream kernel?  Can you share the config and
toolchain versions?

-- 
Josh