linux-kernel - Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore)

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Message-ID: <20180813200359.31311bbb@gandalf.local.home>
Date:   Mon, 13 Aug 2018 20:03:59 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Song Liu <liu.song.a23@...il.com>, srikar@...ux.vnet.ibm.com,
        mhiramat@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, open list <linux-kernel@...r.kernel.org>,
        ananth@...ux.vnet.ibm.com,
        Alexis Berlemont <alexis.berlemont@...il.com>,
        naveen.n.rao@...ux.vnet.ibm.com,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux@...linux.org.uk, ralf@...ux-mips.org, paul.burton@...s.com
Subject: Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference
 count (semaphore)

On Mon, 13 Aug 2018 13:50:19 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> On 08/13, Ravi Bangoria wrote:
> >
> > On 08/11/2018 01:27 PM, Song Liu wrote:  
> > >> +
> > >> +static void delayed_uprobe_delete(struct delayed_uprobe *du)
> > >> +{
> > >> +       if (!du)
> > >> +               return;  
> > > Do we really need this check?  
> >
> > Not necessary though, but I would still like to keep it for a safety.  
> 
> Heh. I tried to ignore all minor problems in this version, but now that Song
> mentioned this unnecessary check...
> 
> Personally I really dislike the checks like this one.
> 
> 	- It can confuse the reader who will try to understand the purpose
> 
> 	- it can hide a bug if delayed_uprobe_delete(du) is actually called
> 	  with du == NULL.
> 
> IMO, you should either remove it and let the kernel crash (to notice the
> problem), or turn it into
> 
> 	if (WARN_ON(!du))
> 		return;

I'd prefer the more robust WARN_ON(!du) above instead of removing it.

-- Steve