linux-kernel - Re: [PATCH v5 1/2] ftrace: disable preemption when recursion locked

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Message-ID: <alpine.LSU.2.21.2110261128120.28494@pobox.suse.cz>
Date:   Tue, 26 Oct 2021 11:35:16 +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>,
        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 v5 1/2] ftrace: disable preemption when recursion
 locked

Hi,

> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
> index abe1a50..2bc1522 100644
> --- a/include/linux/trace_recursion.h
> +++ b/include/linux/trace_recursion.h
> @@ -135,6 +135,9 @@ static __always_inline int trace_get_context_bit(void)
>  # define do_ftrace_record_recursion(ip, pip)	do { } while (0)
>  #endif
> 
> +/*
> + * Preemption is promised to be disabled when return bit > 0.
> + */
>  static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip,
>  							int start)
>  {
> @@ -162,11 +165,17 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign
>  	current->trace_recursion = val;
>  	barrier();
> 
> +	preempt_disable_notrace();
> +
>  	return bit;
>  }
> 
> +/*
> + * Preemption will be enabled (if it was previously enabled).
> + */
>  static __always_inline void trace_clear_recursion(int bit)
>  {
> +	preempt_enable_notrace();
>  	barrier();
>  	trace_recursion_clear(bit);
>  }

The two comments should be updated too since Steven removed the "bit == 0" 
trick.

> @@ -178,7 +187,7 @@ static __always_inline void trace_clear_recursion(int bit)
>   * tracing recursed in the same context (normal vs interrupt),
>   *
>   * Returns: -1 if a recursion happened.
> - *           >= 0 if no recursion
> + *           > 0 if no recursion.
>   */
>  static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
>  							 unsigned long parent_ip)

And this change would not be correct now.

Regards
Miroslav