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Message-ID: <23366389-1be5-92ef-7728-ce639d46a0b0@collabora.com>
Date:   Fri, 26 May 2023 10:45:32 +0200
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Subject: Re: [PATCH] notifier: Initialize new struct srcu_usage field
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To:     Chen-Yu Tsai <wenst@chromium.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mediatek@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org,
        =?UTF-8?Q?N=c3=adcolas_F_=2e_R_=2e_A_=2e_Prado?= 
        <nfraprado@collabora.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
References: <20230526073539.339203-1-wenst@chromium.org>
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
In-Reply-To: <20230526073539.339203-1-wenst@chromium.org>
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Il 26/05/23 09:35, Chen-Yu Tsai ha scritto:
> In commit 95433f726301 ("srcu: Begin offloading srcu_struct fields to
> srcu_update"), a new struct srcu_usage field was added, but was not
> properly initialized. This led to a "spinlock bad magic" BUG when
> the SRCU notifier was ever used. This was observed in the MediaTek
> CCI devfreq driver on next-20230525. Trimmed stack trace as follows:
> 
>      BUG: spinlock bad magic on CPU#4, swapper/0/1
>       lock: 0xffffff80ff529ac0, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
>      Call trace:
>       spin_bug+0xa4/0xe8
>       do_raw_spin_lock+0xec/0x120
>       _raw_spin_lock_irqsave+0x78/0xb8
>       synchronize_srcu+0x3c/0x168
>       srcu_notifier_chain_unregister+0x5c/0xa0
>       cpufreq_unregister_notifier+0x94/0xe0
>       devfreq_passive_event_handler+0x7c/0x3e0
>       devfreq_remove_device+0x48/0xe8
> 
> Add __SRCU_USAGE_INIT() to SRCU_NOTIFIER_INIT() so that srcu_usage gets
> initialized properly.
> 
> Fixes: 95433f726301 ("srcu: Begin offloading srcu_struct fields to srcu_update")
> Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>

Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>