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Date:   Wed, 23 Nov 2022 12:06:13 +0100 (CET)
From:   Anna-Maria Behnsen <anna-maria@linutronix.de>
To:     Thomas Gleixner <tglx@linutronix.de>
cc:     LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linuxfoundation.org>,
        Steven Rostedt <rostedt@goodmis.org>,
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        Stephen Boyd <sboyd@kernel.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Julia Lawall <Julia.Lawall@inria.fr>,
        Arnd Bergmann <arnd@arndb.de>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Marc Zyngier <maz@kernel.org>,
        Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        linux-bluetooth@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org
Subject: Re: [patch V2 12/17] timers: Silently ignore timers with a NULL
 function
In-Reply-To: <20221122173648.793640919@linutronix.de>
Message-ID: <165dcea1-2713-218b-fecf-5bf80452229@linutronix.de>
References: <20221122171312.191765396@linutronix.de> <20221122173648.793640919@linutronix.de>
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On Tue, 22 Nov 2022, Thomas Gleixner wrote:

> Tearing down timers which have circular dependencies to other
> functionality, e.g. workqueues, where the timer can schedule work and work
> can arm timers is not trivial.
> 
> In those cases it is desired to shutdown the timer in a way which prevents
> rearming of the timer. The mechanism to do so it to set timer->function to
> NULL and use this as an indicator for the timer arming functions to ignore
> the (re)arm request.
> 
> In preparation for that replace the warnings in the relevant code pathes
> with checks for timer->function == NULL and discard the rearm request
> silently.
> 
> Add debug_assert_init() instead of the WARN_ON_ONCE(!timer->function)
> checks so that debug objects can warn about non-initialized timers.

Could you expand this paragraph, so that is is not missleading when a
reader is not aware of the details of debug objects? Otherwise it seems to
the reader that debug objects will warn when timer->function == NULL.

  The warning of debug objects does not cover the original
  WARN_ON_ONCE(!timer->function). It warns when timer was not initialized
  using timer_setup[_on_stack]() or via DEFINE_TIMER().


> If developers fail to enable debug objects and then waste lots of time to
> figure out why their non-initialized timer is not firing, they deserve it.


Thanks,

	Anna-Maria