linux-kernel - Re: [PATCH] arm64: ftrace: stop using kstop

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Message-ID: <20151128105819.3451ab3e@grimm.local.home>
Date:	Sat, 28 Nov 2015 10:58:19 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Li Bin <huawei.libin@...wei.com>
Cc:	<mingo@...hat.com>, <catalin.marinas@....com>,
	<will.deacon@....com>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <guohanjun@...wei.com>,
	<dingtianhong@...wei.com>
Subject: Re: [PATCH] arm64: ftrace: stop using kstop_machine to
 enable/disable tracing

On Sat, 28 Nov 2015 15:50:09 +0800
Li Bin <huawei.libin@...wei.com> wrote:

> On arm64, kstop_machine which is hugely disruptive to a running
> system is not needed to convert nops to ftrace calls or back,
> because that modifed code is a single 32bit instructions which
> is impossible to cross cache (or page) boundaries, and the used str
> instruction is single-copy atomic.

Is this really true? I thought that arm (and then perhaps arm64) has
some 2 byte instructions. If that's the case it is very well possible
that a 4 byte instruction can cross cache lines.

-- Steve

> 
> Cc: <stable@...r.kernel.org> # 3.18+
> Signed-off-by: Li Bin <huawei.libin@...wei.com>
> ---
>  arch/arm64/kernel/ftrace.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
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