linux-kernel - Re: [PATCH v4 1/2] rcu: Make expedited RCU CPU stall warnings detect stall-end races

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Message-ID: <20251231171317.GBaVVZreLiknrb8zWT@fat_crate.local>
Date: Wed, 31 Dec 2025 18:13:17 +0100
From: Borislav Petkov <bp@...en8.de>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: rcu@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	rostedt@...dmis.org
Subject: Re: [PATCH v4 1/2] rcu: Make expedited RCU CPU stall warnings detect
 stall-end races

On Mon, Dec 29, 2025 at 11:16:15AM -0800, Paul E. McKenney wrote:
> If an expedited RCU CPU stall ends just at the stall-warning timeout,
> the current code will print an expedited stall-warning message, but one
> that doesn't identify any CPUs or tasks causing the stall.  This is most
> likely to happen for short-timeout stalls, for example, the 20-millisecond
> timeouts that are sometimes used for small embedded devices.  Needless to
> say, these semi-empty stall-warning messages can be rather confusing.
> 
> One option would be to suppress the stall-warning message entirely in
> this case, but the near-miss information can be quite valuable.
> 
> This commit therefore detects this race condition and emits a "INFO:

s/This commit therefore detects this/Detect this/

> Expedited stall ended before state dump start" message to clarify matters.
> 
> Reported-by: Borislav Petkov <bp@...en8.de>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---
>  kernel/rcu/tree_exp.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)

But yeah, makes sense.

Acked-by: Borislav Petkov (AMD) <bp@...en8.de>

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette