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

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Message-ID: <YLY0INyDtfjgVrXv@hirez.programming.kicks-ass.net>
Date:   Tue, 1 Jun 2021 15:20:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     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, 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?