linux-kernel - Re: [patch V3 24/32] jump_label: Reorder hotplug lock and jump_label

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Message-Id: <20170524.085044.1007416544464954756.davem@davemloft.net>
Date:   Wed, 24 May 2017 08:50:44 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...nel.org, rostedt@...dmis.org, bigeasy@...utronix.de,
        paulmck@...ux.vnet.ibm.com, ralf@...ux-mips.org,
        cmetcalf@...lanox.com, jbaron@...mai.com
Subject: Re: [patch V3 24/32] jump_label: Reorder hotplug lock and
 jump_label_lock

From: Thomas Gleixner <tglx@...utronix.de>
Date: Wed, 24 May 2017 10:15:35 +0200

> The conversion of the hotplug locking to a percpu rwsem unearthed lock
> ordering issues all over the place.
> 
> The jump_label code has two issues:
> 
>  1) Nested get_online_cpus() invocations
> 
>  2) Ordering problems vs. the cpus rwsem and the jump_label_mutex
> 
> To cure these, the following lock order has been established;
> 
>    cpus_rwsem -> jump_label_lock -> text_mutex
> 
> Even if not all architectures need protection against CPU hotplug, taking
> cpus_rwsem before jump_label_lock is now mandatory in code pathes which
> actually modify code and therefor need text_mutex protection.
> 
> Move the get_online_cpus() invocations into the core jump label code and
> establish the proper lock order where required.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Acked-by: David S. Miller <davem@...emloft.net>