linux-kernel - Re: [PATCH 08/19] perf tools: Add mem2node object

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Date:   Thu, 8 Mar 2018 14:18:09 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 08/19] perf tools: Add mem2node object

On Thu, Mar 08, 2018 at 09:58:49AM -0300, Arnaldo Carvalho de Melo wrote:

SNIP

> > I don't think we need nentries.. AFAIK realloc works ok over single variable
> 
> So:
> 
> 1) you alloc entries with a max number of entries
> 
> 2) you go on populating it
> 
> 3) there are some left, lets shrink it:
> 
> 	entries = realloc(entries, nr_entries * sizeof(entries[0]);
> 
> Here it will probably not fail, but you check it anyway, and that is
> right, what happens if this returns NULL? entries gets set to NULL,
> we lose the reference to the allocated memory and you return -ENOMEM,
> right?
> 
> We end up leaking entries when what I'm suggesting you to do is to
> not clobber entries with the return of realloc() (doing it this way most
> of the time leads to bugs), but instead store it to a temp var
> (nentries), and if it succeeds, then you know that you can
> set nentries to entries and go ahead with your nicely shrunk block of
> memory.
> 
> If it fails, then you continue with the original block of memory, that
> continues to have what you just set up, etc.

ah that ;-) ok, will fix

thanks,
jirka