linux-kernel - Re: [PATCH] notifier: Initialize new struct srcu

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Date:   Fri, 26 May 2023 10:45:32 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chen-Yu Tsai <wenst@...omium.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Nícolas F . R . A . Prado 
        <nfraprado@...labora.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] notifier: Initialize new struct srcu_usage field

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@...omium.org>

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