linux-kernel - Re: [PATCH -tip v3 6/7] kprobes/x86: Remove disable

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Date:   Thu, 28 Sep 2017 23:48:18 -0700
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     mingo@...hat.com, x86@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexei Starovoitov <ast@...com>
Subject: Re: [PATCH -tip v3 6/7] kprobes/x86: Remove disable_irq from
 ftrace-based/optimized kprobe

On Thu, 28 Sep 2017 09:25:41 +0200
Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > Actually kprobes doesn't need to disable irq if it is
> > called from ftrace/jump trampoline code because
> > Documentation/kprobes.txt says
> > 
> > -----
> > Probe handlers are run with preemption disabled.  Depending on the
> > architecture and optimization state, handlers may also run with
> > interrupts disabled (e.g., kretprobe handlers and optimized kprobe
> > handlers run without interrupt disabled on x86/x86-64).
> > -----
> > 
> > So let's remove irq disabling from those handlers.
> 
> > -	local_irq_save(flags);
> 
> The title is talking about disable_irq():
> 
>   kprobes/x86: Remove disable_irq from ftrace-based/optimized kprobe
> 
> ... but the patch is actually using local_irq_save(), which is an entirely 
> different thing! You probably wanted to say:
> 
>   kprobes/x86: Remove irq disabling from ftrace-based/optimized kprobes

Correct! That's my mistake. thanks!

> 
> Also note the plural of 'kprobes' when we refer to them as a generic thing.
> 
> I fixed the title, but _please_ read changelogs more carefully before sending 
> them.

Thank you again,

> 
> Thanks,
> 
> 	Ingo


-- 
Masami Hiramatsu <mhiramat@...nel.org>