linux-kernel - Re: [PATCH v3 1/2] ftrace: disable preemption between ftrace_test_recursion

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Message-ID: <alpine.LSU.2.21.2110141108150.23710@pobox.suse.cz>
Date:   Thu, 14 Oct 2021 11:13:13 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     王贇 <yun.wang@...ux.alibaba.com>
cc:     Guo Ren <guoren@...nel.org>, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Colin Ian King <colin.king@...onical.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Jisheng Zhang <jszhang@...nel.org>, linux-csky@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        live-patching@...r.kernel.org
Subject: Re: [PATCH v3 1/2] ftrace: disable preemption between
 ftrace_test_recursion_trylock/unlock()

> diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c
> index e8029ae..b8d75fb 100644
> --- a/kernel/livepatch/patch.c
> +++ b/kernel/livepatch/patch.c
> @@ -49,14 +49,16 @@ static void notrace klp_ftrace_handler(unsigned long ip,
> 
>  	ops = container_of(fops, struct klp_ops, fops);
> 
> +	/*
> +	 *

This empty line is not useful.

> +	 * The ftrace_test_recursion_trylock() will disable preemption,
> +	 * which is required for the variant of synchronize_rcu() that is
> +	 * used to allow patching functions where RCU is not watching.
> +	 * See klp_synchronize_transition() for more details.
> +	 */
>  	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().
> -	 */
> -	preempt_disable_notrace();
> 
>  	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
>  				      stack_node);
> @@ -120,7 +122,6 @@ static void notrace klp_ftrace_handler(unsigned long ip,
>  	klp_arch_set_pc(fregs, (unsigned long)func->new_func);
> 
>  unlock:
> -	preempt_enable_notrace();
>  	ftrace_test_recursion_unlock(bit);
>  }

Acked-by: Miroslav Benes <mbenes@...e.cz>

for the livepatch part of the patch.

I would also ask you not to submit new versions so often, so that the 
other reviewers have time to actually review the patch set.

Quoting from Documentation/process/submitting-patches.rst:

"Wait for a minimum of one week before resubmitting or pinging reviewers - 
possibly longer during busy times like merge windows."

Thanks

Miroslav