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From: Thomas Gleixner <tglx@linutronix.de>
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To: Benjamin Segall <bsegall@google.com>, linux-kernel@vger.kernel.org,
 Anna-Maria Behnsen <anna-maria@linutronix.de>, Frederic
 Weisbecker <frederic@kernel.org>
Subject: Re: [PATCH v2] posix-cpu-timers: clear TICK_DEP_BIT_POSIX_TIMER on
 clone
In-Reply-To: <xm26ttd9ay34.fsf@google.com>
References: <xm26ttd9ay34.fsf@google.com>
Date: Sat, 19 Oct 2024 22:59:04 +0200
Message-ID: <8734kr95d3.ffs@tglx>
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On Fri, Oct 18 2024 at 14:41, Benjamin Segall wrote:
> When we clone a new thread, we do not inherit its posix_cputimers, and

We? We neither clone something nor can we inherit anything from the
kernel. Please do not impersonate code and use passive voice.

> clear them with posix_cputimers_init. However, this does not clear the

Please denote functions with brackets, i.e. fun() so its obvious.

> tick dependency it creates in tsk->tick_dep_mask, and the handler does
> not reach the code to clear the dependency if there were no timers to
> begin with.
>
> Thus if a thread has a cputimer running before cloneing/forking, that
> hierarchy will prevent nohz_full unless they create a cputimer of their
> own.
>
> Process-wide timers do not have this problem because fork does not copy
> signal_struct as a baseline, it creates one from scratch.

And the solution to this is described where in the change log?

Thanks,

        tglx