linux-kernel - Re: [PATCH v9] watchdog/hardlockup: simplify perf event probe and remove per-cpu dependency

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAD=FV=VpV19wB5uGUCRDnCO_SktL3Svnh3V+NT5oNji70Ff3pw@mail.gmail.com>
Date: Thu, 29 Jan 2026 08:18:09 -0800
From: Doug Anderson <dianders@...omium.org>
To: Qiliang Yuan <realwujing@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>, Li Huafei <lihuafei1@...wei.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Jinchao Wang <wangjinchao600@...il.com>, 
	Yicong Yang <yangyicong@...ilicon.com>, Thorsten Blum <thorsten.blum@...ux.dev>, 
	linux-watchdog@...r.kernel.org, mm-commits@...r.kernel.org, 
	Shouxin Sun <sunshx@...natelecom.cn>, Junnan Zhang <zhangjn11@...natelecom.cn>, 
	Qiliang Yuan <yuanql9@...natelecom.cn>, Song Liu <song@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9] watchdog/hardlockup: simplify perf event probe and
 remove per-cpu dependency

Hi,

On Wed, Jan 28, 2026 at 6:26 PM Qiliang Yuan <realwujing@...il.com> wrote:
>
> Simplify the hardlockup detector's probe path and remove its implicit
> dependency on pinned per-cpu execution.
>
> Refactor hardlockup_detector_event_create() to be stateless. Return
> the created perf_event pointer to the caller instead of directly
> modifying the per-cpu 'watchdog_ev' variable. This allows the probe
> path to safely manage a temporary event without the risk of leaving
> stale pointers should task migration occur.
>
> Signed-off-by: Shouxin Sun <sunshx@...natelecom.cn>
> Signed-off-by: Junnan Zhang <zhangjn11@...natelecom.cn>
> Signed-off-by: Qiliang Yuan <yuanql9@...natelecom.cn>
> Signed-off-by: Qiliang Yuan <realwujing@...il.com>
> Cc: Douglas Anderson <dianders@...omium.org>
> Cc: Song Liu <song@...nel.org>
> Cc: Jinchao Wang <wangjinchao600@...il.com>
> ---
> v9:
> - remove unused `#include <linux/cpu.h>`
> v8:
> - Add Signed-off-by with work email.
> v7:
> - Update Signed-off-by to match author email.
> - Remove redundant cpu_hotplug_disable() in probe path.
> v6:
> - Change title to "simplify/cleanup" and remove "Fixes" tag since the issue
>   is not reproducible on mainline.
> - Rewrite commit message in imperative mood.
> - Clarify that mainline is safe while this improves robustness.
> v5:
> - Refine description: clarify that the retry path uses worker threads
>   without PF_PERCPU_THREAD (though mainline is safe due to system_percpu_wq).
> v4:
> - Add cpu_hotplug_disable() in watchdog_hardlockup_probe() to stabilize
>   the probe CPU.
> - Update description to explain the relevance of 4.19 logs.
> v3:
> - Refactor hardlockup_detector_event_create() to be stateless by returning
>   the event pointer instead of directly assigning to per-cpu variables.
> - Restore PMU cycle fallback and unify the enable/probe paths.
> v2:
> - Add Cc: stable@...r.kernel.org.
> v1:
> - Avoid 'watchdog_ev' in probe path by manually creating and releasing a
>   local perf event.
>
>  kernel/watchdog_perf.c | 50 +++++++++++++++++++++++-------------------
>  1 file changed, 28 insertions(+), 22 deletions(-)

Since I previously gave you my Reviewed-by tag and the changes you
made were minor (and exactly what I requested when I gave you my tag),
you should have kept my Reviewed-by tag in your v9. In general,
knowing whether to keep someone's Reviewed-by or Tested-by tag when
sending a new version is a bit of a judgement call, but in this case
it should have been pretty clear. Generally, if you remove someone's
tag that was given before it's good to mention "after the cut" why you
removed it. If you are unsure about keeping a tag but still decide to
keep it, you can still call attention to that fact "after the cut".

In any case:

Reviewed-by: Douglas Anderson <dianders@...omium.org>

No need to send a v10 adding that tag unless other changes are needed.
Andrew will add it when landing.

-Doug