Re: [PATCH v4] tracing: ring-buffer: fix stale reader-page link

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] tracing: ring-buffer: reply text in changelog and missing Fixes
  trailer
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commit c4296f8629e0420816a4b5f1c95a30a1141d5523
Author: Haoli Zhang <26031212468@stu.xidian.edu.cn>

> tracing: ring-buffer: fix stale reader-page link
>
> Hi Steve,
>
> Thanks for reviewing v3. I apologize for adding unnecessary NMI reader
> coordination and skip handling. You noted the report is unrelated to NMI
> reads. The lockless NMI path is only a best-effort crash-dump path.
> I have removed that complexity and dropped the Fixes tag.
>
> The report shows rb_is_reader_page() dereferencing a freed page through
> page->list.prev->next. During shrink, reader_page is detached from the
> ring list and can retain a previous link to a page being removed. Redirect
> that link to the surviving tail page while identifying pages to remove,
> before any removed page is freed.
>
> This change does not add work to the normal writer fast path or alter NMI
> reader behavior.
>
> Reported-by: syzbot+37e1793bdb0061ea3a47@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=37e1793bdb0061ea3a47
> Co-developed-by: Jinning Zhang <25031212117@stu.xidian.edu.cn>
> Signed-off-by: Jinning Zhang <25031212117@stu.xidian.edu.cn>
> Co-developed-by: Bin Yu <byu@xidian.edu.cn>
> Signed-off-by: Bin Yu <byu@xidian.edu.cn>
> Signed-off-by: Haoli Zhang <26031212468@stu.xidian.edu.cn>

[Severity: Low]
The opening paragraph ("Hi Steve, ...") is a personal reply to a reviewer
and should go below the "---" separator line so it is not recorded in git
history.

Also, since commit 83f40318dab0 ("ring-buffer: Make removal of ring buffer
pages atomic") rewrote rb_remove_pages() to unlink pages in place without
calling rb_reset_cpu() to reinitialize cpu_buffer->reader_page->list,
should this include:

  Fixes: 83f40318dab0 ("ring-buffer: Make removal of ring buffer pages atomic")

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Sashiko AI review · https://sashiko.dev/#/patchset/20261113033612.1349-1-26031212468@stu.xidian.edu.cn?part=1