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From: Steven Rostedt <rostedt@goodmis.org>
To: 王贇 <yun.wang@linux.alibaba.com>
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
Subject: Re: [PATCH 1/2] ftrace: disable preemption on the testing of recursion
Date: Tue, 12 Oct 2021 08:43:31 -0400	[thread overview]
Message-ID: <20211012084331.06b8dd23@gandalf.local.home> (raw)
In-Reply-To: <a8756482-024c-c858-b3d1-1ffa9a5eb3f7@linux.alibaba.com>

On Tue, 12 Oct 2021 13:40:08 +0800
王贇 <yun.wang@linux.alibaba.com> wrote:

> --- a/include/linux/trace_recursion.h
> +++ b/include/linux/trace_recursion.h
> @@ -214,7 +214,14 @@ static __always_inline void trace_clear_recursion(int bit)
>  static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
>  							 unsigned long parent_ip)
>  {
> -	return trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX);
> +	int bit;
> +
> +	preempt_disable_notrace();

The recursion test does not require preemption disabled, it uses the task
struct, not per_cpu variables, so you should not disable it before the test.

	bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX);
	if (bit >= 0)
		preempt_disable_notrace();

And if the bit is zero, it means a recursion check was already done by
another caller (ftrace handler does the check, followed by calling perf),
and you really don't even need to disable preemption in that case.

	if (bit > 0)
		preempt_disable_notrace();

And on the unlock, have:

 static __always_inline void ftrace_test_recursion_unlock(int bit)
 {
	if (bit)
		preempt_enable_notrace();
 	trace_clear_recursion(bit);
 }

But maybe that's over optimizing ;-)

-- Steve


> +	bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START, TRACE_FTRACE_MAX);
> +	if (bit < 0)
> +		preempt_enable_notrace();
> +
> +	return bit;
>  }


  parent reply	other threads:[~2021-10-12 12:43 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-12  5:39 [PATCH 0/2] ftrace: make sure preemption disabled on recursion testing 王贇
2021-10-12  5:40 ` [PATCH 1/2] ftrace: disable preemption on the testing of recursion 王贇
2021-10-12 12:17   ` Steven Rostedt
2021-10-13  1:46     ` 王贇
2021-10-12 12:24   ` Miroslav Benes
2021-10-12 12:29     ` Steven Rostedt
2021-10-13  1:52       ` 王贇
2021-10-13  1:50     ` 王贇
2021-10-13  2:27       ` Steven Rostedt
2021-10-13  2:36         ` 王贇
2021-10-12 12:43   ` Steven Rostedt [this message]
2021-10-13  2:04     ` 王贇
2021-10-13  2:30       ` Steven Rostedt
2021-10-13  2:38         ` 王贇
2021-10-12  5:40 ` [PATCH 2/2] ftrace: prevent preemption in perf_ftrace_function_call() 王贇
2021-10-12 11:20   ` Peter Zijlstra
2021-10-13  1:45     ` 王贇
2021-10-12  5:41 ` [PATCH 0/2] ftrace: make sure preemption disabled on recursion testing 王贇
2021-10-13  3:16 ` [PATCH v2 0/2] fix & prevent the missing preemption disabling 王贇
2021-10-13  3:17   ` [PATCH v2 1/2] ftrace: disable preemption between ftrace_test_recursion_trylock/unlock() 王贇
2021-10-13  3:18   ` [PATCH v2 2/2] ftrace: do CPU checking after preemption disabled 王贇
2021-10-13  3:26   ` [PATCH v2 0/2] fix & prevent the missing preemption disabling Steven Rostedt
2021-10-13  3:33     ` 王贇
2021-10-26 23:48 ` [PATCH 0/2] ftrace: make sure preemption disabled on recursion testing Palmer Dabbelt

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