Re: [PATCH] mce: fix missing stack-dumping in mce_panic()

[Tony Luck]

On Sat, Dec 03, 2022 at 10:19:32AM +0800, Miaohe Lin wrote:
> So I think it's better to have at least one stack dumps. Also what the commit
> 6e6f0a1f0fa6 ("panic: don't print redundant backtraces on oops") and commit
> 026ee1f66aaa ("panic: fix stack dump print on direct call to panic()") want
> to do is avoiding nested stack-dumping to have the original oops data being
> scrolled away on a 80x50 screen but to have *at least one backtraces*. So
> this patch acts more like a BUGFIX to ensure having at least one backtraces
> in mce_panic(). What's your thought, Luck?

I tried out your patch with the ras-tools test:

# ./einj_mem_uc -f copyout

which currently causes a panic from the "recoverable" machine check.

Your patch worked fine:

[  112.457735] stack backtrace:
[  112.457736] CPU: 124 PID: 3401 Comm: einj_mem_uc Not tainted 6.1.0-rc7+ #41
[  112.457738] Hardware name: Intel Corporation PURLEY/PURLEY, BIOS PLYDCRB1.86B.0154.R04.1804231104 04/23/2018
[  112.457739] Call Trace:
[  112.457740]  <#MC>
[  112.457742]  dump_stack_lvl+0x5a/0x78
[  112.457746]  dump_stack+0x10/0x16
[  112.457748]  print_usage_bug.part.0+0x1ad/0x1c4
[  112.457755]  lock_acquire.cold+0x16/0x47
[  112.457759]  ? down_trylock+0x14/0x40
[  112.457762]  ? panic+0x180/0x2b9
[  112.457766]  _raw_spin_lock_irqsave+0x4e/0x70
[  112.457768]  ? down_trylock+0x14/0x40
[  112.457771]  down_trylock+0x14/0x40
[  112.457772]  ? panic+0x180/0x2b9
[  112.457775]  __down_trylock_console_sem+0x34/0xc0
[  112.457778]  console_unblank+0x1d/0x90
[  112.457781]  panic+0x180/0x2b9
[  112.457788]  mce_panic+0x118/0x1e0
[  112.457794]  do_machine_check+0x79a/0x890
[  112.457800]  ? copy_user_enhanced_fast_string+0xa/0x50
[  112.457810]  exc_machine_check+0x76/0xb0
[  112.457813]  asm_exc_machine_check+0x1a/0x40
[  112.457816] RIP: 0010:copy_user_enhanced_fast_string+0xa/0x50
[  112.457819] Code: d1 f3 a4 31 c0 0f 01 ca c3 cc cc cc cc 8d 0c ca 89 ca eb 2c 66 66 2e 0f 1f 84 00 00 00 00 00 90 0f 01 cb 83 fa 40 72 48 89 d1 <f3> a4 31 c0 0f 01 ca c3 cc cc cc cc 89 ca eb 06 66 0f 1f 44 00 00
[  112.457820] RSP: 0018:ffffb140f789bbd8 EFLAGS: 00050206
[  112.457822] RAX: 0000000000001000 RBX: ffffb140f789be58 RCX: 0000000000000c00
[  112.457824] RDX: 0000000000001000 RSI: ffff9133eb3f0400 RDI: 000055c1a36986c0
[  112.457825] RBP: ffffb140f789bc68 R08: 00000000f789be01 R09: 0000000000001000
[  112.457827] R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000001000
[  112.457828] R13: ffff9133eb3f0000 R14: 0000000000001000 R15: 0000000000000000
[  112.457837]  </#MC>
[  112.457838]  <TASK>
[  112.457838]  ? _copy_to_iter+0xc3/0x6f0
[  112.457843]  ? filemap_get_pages+0x9b/0x670
[  112.457851]  copy_page_to_iter+0x7c/0x1f0
[  112.457854]  ? find_held_lock+0x31/0x90
[  112.457858]  filemap_read+0x1ec/0x390
[  112.457865]  ? __fsnotify_parent+0x10f/0x310
[  112.457867]  ? aa_file_perm+0x1ab/0x610
[  112.457875]  generic_file_read_iter+0xf4/0x170
[  112.457879]  ext4_file_read_iter+0x5b/0x1e0
[  112.457881]  ? security_file_permission+0x4e/0x60
[  112.457886]  vfs_read+0x208/0x2e0
[  112.457895]  ksys_read+0x6d/0xf0
[  112.457900]  __x64_sys_read+0x19/0x20
[  112.457902]  do_syscall_64+0x38/0x90
[  112.457906]  entry_SYSCALL_64_after_hwframe+0x63/0xcd


Tested-by: Tony Luck <tony.luck@xxxxxxxxx>

-Tony