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Date:   Mon, 11 Jul 2022 10:32:35 -0700
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Aaron Tomlin <atomlin@redhat.com>
Cc:     rostedt@goodmis.org, cl@linux.com, pmladek@suse.com,
        mbenes@suse.cz, christophe.leroy@csgroup.eu,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-modules@vger.kernel.org, atomlin@atomlin.com,
        ghalat@redhat.com, oleksandr@natalenko.name, neelx@redhat.com,
        daniel.thompson@linaro.org, hch@infradead.org, tglx@linutronix.de,
        adrian.hunter@intel.com, linux-rt-users@vger.kernel.org
Subject: Re: [PATCH v3 -next 1/1] module: kallsyms: Ensure preemption in
 add_kallsyms() with PREEMPT_RT
Message-ID: <Ysxes81GjdNK3yE+@bombadil.infradead.org>
References: <20220711171719.1244255-1-atomlin@redhat.com>
 <20220711171719.1244255-2-atomlin@redhat.com>
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On Mon, Jul 11, 2022 at 06:17:19PM +0100, Aaron Tomlin wrote:
> The commit 08126db5ff73 ("module: kallsyms: Fix suspicious rcu usage")
> under PREEMPT_RT=y, disabling preemption introduced an unbounded
> latency since the loop is not fixed. This change caused a regression
> since previously preemption was not disabled and we would dereference
> RCU-protected pointers explicitly. That being said, these pointers
> cannot change.
> 
> Before kallsyms-specific data is prepared/or set-up, we ensure that
> the unformed module is known to be unique i.e. does not already exist
> (see load_module()). Therefore, we can fix this by using the common and
> more appropriate RCU flavour as this section of code can be safely
> preempted.
> 
> Reported-by: Steven Rostedt <rostedt@goodmis.org>
> Fixes: 08126db5ff73 ("module: kallsyms: Fix suspicious rcu usage")
> Signed-off-by: Aaron Tomlin <atomlin@redhat.com>

Thanks! Queued up!

  Luis