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Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of
 recursion
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Guo Ren <guoren@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
        Helge Deller <deller@gmx.de>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jiri Kosina <jikos@kernel.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Petr Mladek <pmladek@suse.com>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Colin Ian King <colin.king@canonical.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Jisheng Zhang <jszhang@kernel.org>, linux-csky@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
        live-patching@vger.kernel.org
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From:   =?UTF-8?B?546L6LSH?= <yun.wang@linux.alibaba.com>
Message-ID: <d079d249-b603-230a-a905-3f0df55056ae@linux.alibaba.com>
Date:   Wed, 13 Oct 2021 09:46:42 +0800
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On 2021/10/12 下午8:17, Steven Rostedt wrote:
> On Tue, 12 Oct 2021 13:40:08 +0800
> 王贇 <yun.wang@linux.alibaba.com> wrote:
> 
>> @@ -52,11 +52,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>>  	bit = ftrace_test_recursion_trylock(ip, parent_ip);
>>  	if (WARN_ON_ONCE(bit < 0))
>>  		return;
>> -	/*
>> -	 * A variant of synchronize_rcu() is used to allow patching functions
>> -	 * where RCU is not watching, see klp_synchronize_transition().
>> -	 */
> 
> I have to take a deeper look at this patch set, but do not remove this
> comment, as it explains the protection here, that is not obvious with the
> changes you made.

Will keep that in v2.

Regards,
Michael Wang

> 
> -- Steve
> 
> 
>> -	preempt_disable_notrace();
>>
>>  	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
>>  				      stack_node);