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From:   Sven Schnelle <svens@linux.ibm.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org
Subject: Re: ftrace startup tests crashing due to missing rcu_synchronize()
References: <yt9dilte4px4.fsf@linux.ibm.com>
        <20220216135419.01d96fe1@gandalf.local.home>
        <20220216135821.67a22c52@gandalf.local.home>
Date:   Wed, 16 Feb 2022 20:31:37 +0100
In-Reply-To: <20220216135821.67a22c52@gandalf.local.home> (Steven Rostedt's
        message of "Wed, 16 Feb 2022 13:58:21 -0500")
Message-ID: <yt9da6eq4nhi.fsf@linux.ibm.com>
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Steven Rostedt <rostedt@goodmis.org> writes:

> On Wed, 16 Feb 2022 13:54:19 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
>> That is, shutdown is called, the item is removed from the list and freed,
>> but something got preempted while on the ftrace trampoline, with a
>> reference to the item, and then woke up and executed the item that was
>> freed.
>> 
>> I'll look into it. Thanks for the report.
>
> OK, I wonder if something changed with "is_kernel_core_date()"?
>
> Because on registering, we have:
>
> 	if (!is_kernel_core_data((unsigned long)ops))
> 		ops->flags |= FTRACE_OPS_FL_DYNAMIC;

I checked, and the flag gets set here. I cannot say whether it
is also set when the system crashes, but i would expect it.