linux-kernel - Re: [PATCH] kprobes: Do not increment probe miss count in the fault handler

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Message-Id: <20210602084850.598a60d848a7bdc7c3b0085a@kernel.org>
Date:   Wed, 2 Jun 2021 08:48:50 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        mhiramat@...nel.org, ananth@...ux.ibm.com,
        Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        mingo@...nel.org, rostedt@...dmis.org, x86@...nel.org
Subject: Re: [PATCH] kprobes: Do not increment probe miss count in the fault
 handler

On Tue, 1 Jun 2021 15:20:32 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Jun 01, 2021 at 05:31:50PM +0530, Naveen N. Rao wrote:
> > Kprobes has a counter 'nmissed', that is used to count the number of
> > times a probe handler was not called. This generally happens when we hit
> > a kprobe while handling another kprobe.
> > 
> > However, if one of the probe handlers causes a fault, we are currently
> > incrementing 'nmissed'. The comment in fault handler indicates that this
> > can be used to account faults taken by the probe handlers. But, this has
> > never been the intention as is evident from the comment above 'nmissed'
> > in 'struct kprobe':
> > 
> > 	/*count the number of times this probe was temporarily disarmed */
> > 	unsigned long nmissed;
> > 
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> > ---
> > I'm posting this here so that these can go together, if the patch is ok 
> > otherwise.
> 
> I had the other two queued in perf/core and was about to push then to
> tip, Masami are you good with adding this on top?

Yes, those looks good to me too.

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thank you,

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