Re: [syzbot] [kernel?] WARNING in do_clear_cpu_cap

[Andrew Morton]

On Fri, 31 Jul 2026 10:13:34 -0700 syzbot <syzbot+6cdbd5e494b199d820c3@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> syzbot found the following issue on:
> 
> HEAD commit:    11028ab62899 Merge tag 'probes-fixes-v7.2-rc5' of git://gi..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14e3d9b9580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cb17729fb04b1e3a
> dashboard link: https://syzkaller.appspot.com/bug?extid=6cdbd5e494b199d820c3
> compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13b271b9580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=118a97b1580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/bc967be819a3/disk-11028ab6.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/6e9f003c9cc8/vmlinux-11028ab6.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/5c292926486f/bzImage-11028ab6.xz
> 
> The issue was bisected to:
> 
> commit 684826f8271ad97580b138b9ffd462005e470b99
> Author: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> Date:   Wed Sep 11 02:54:56 2024 +0000
> 
>     zram: free secondary algorithms names

Thanks.  I don't see how zram could have caused this.

fwiw (which might not be a lot), Gemini concluded


Core Issue & Summary

  Root Cause: CPU capability clearing (clear_cpu_cap /
  setup_clear_cpu_cap) was executed during late CPU feature detection
  on a secondary core (identify_secondary_cpu()) after kernel
  alternatives patching was finalized (alternatives_patched == true).

Fix Location:

  The bug needs to be addressed in arch/x86/kernel/cpu/intel.c
  (specifically around early_init_intel()) by ensuring that capability
  overrides/clears are done prior to alternative patching or handled
  via per-CPU feature suppression mechanisms that don't invoke full
  feature mask clearing post-patching.

https://gemini.google.com/share/0cdd1930799f?skid=006fb41e-8e42-4330-9f52-62c4cf089ce0