linux-kernel - Re: [PATCH 01/20] perf nsinfo: fix refcounting

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Date:   Thu, 15 Jul 2021 16:20:24 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Riccardo Mancini <rickyman7@...il.com>,
        Krister Johansen <kjlx@...pleofstupid.com>
Cc:     Ian Rogers <irogers@...gle.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 01/20] perf nsinfo: fix refcounting

Em Thu, Jul 15, 2021 at 04:02:16PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Jul 15, 2021 at 06:07:06PM +0200, Riccardo Mancini escreveu:
> > ASan reports a memory leak of nsinfo during the execution of the perf
> > test "31: Lookup mmap thread".
> > The leak is caused by a refcounted variable being replaced without
> > dropping the refcount.

> > This patch makes sure that the refcnt of nsinfo is decreased whenever
> > a refcounted variable is replaced with a new value.

> So, there are multiple fixes in just one patch, I'll split it into
> three, no need to resend.

> I'll try and check if finding Fixes: for the three is easy, that way
> stable@...r.kernel.org will figure out which of the supported releases
> need each of them.

The second is at the end of this message, and looking at it I think
there is a problem with where this nsinfo reference is stored, it should
be in the 'struct map', that is per-thread, not in the 'struct dso',
that may be shared by multiple 'struct map's in different cgroups, so we
can't set dso->nsinfo in map__new(), right? Kristen?

- Arnaldo

commit 280f3933661f9ca9563ed04ce82313fdbcbb8f75
Author: Riccardo Mancini <rickyman7@...il.com>
Date:   Thu Jul 15 18:07:06 2021 +0200

    perf map: Fix dso->nsinfo refcounting
    
    ASan reports a memory leak of nsinfo during the execution of
    
      # perf test "31: Lookup mmap thread"
    
    The leak is caused by a refcounted variable being replaced without
    dropping the refcount.
    
    This patch makes sure that the refcnt of nsinfo is decreased whenever a
    refcounted variable is replaced with a new value.
    
    Signed-off-by: Riccardo Mancini <rickyman7@...il.com>
    Fixes: bf2e710b3cb8445c ("perf maps: Lookup maps in both intitial mountns and inner mountns.")
    Cc: Ian Rogers <irogers@...gle.com>
    Cc: Jiri Olsa <jolsa@...hat.com>
    Cc: Krister Johansen <kjlx@...pleofstupid.com>
    Cc: Mark Rutland <mark.rutland@....com>
    Cc: Namhyung Kim <namhyung@...nel.org>
    Cc: Peter Zijlstra <peterz@...radead.org>
    Link: http://lore.kernel.org/lkml/55223bc8821b34ccb01f92ef1401c02b6a32e61f.1626343282.git.rickyman7@gmail.com
    Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>

diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
index 8af693d9678cefe0..72e7f3616157ead4 100644
--- a/tools/perf/util/map.c
+++ b/tools/perf/util/map.c
@@ -192,6 +192,8 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
 			if (!(prot & PROT_EXEC))
 				dso__set_loaded(dso);
 		}
+
+		nsinfo__put(dso->nsinfo);
 		dso->nsinfo = nsi;
 
 		if (build_id__is_defined(bid))