linux-kernel - [PATCH] perf: do not flush maps on COMM for perf report

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Date:	Tue, 21 Aug 2012 14:52:20 -0700
From:	Luigi Semenzato <semenzato@...omium.org>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Stephen Wilson <wilsons@...rt.ca>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Ahern <dsahern@...il.com>,
	Namhyung Kim <namhyung@...il.com>,
	Robert Richter <robert.richter@....com>,
	linux-kernel@...r.kernel.org
Cc:	sonnyrao@...omium.org, olofj@...omium.org, eranian@...gle.com,
	Luigi Semenzato <semenzato@...omium.org>
Subject: [PATCH] perf: do not flush maps on COMM for perf report

This fixes a long-standing bug caused by the lack of separate
COMM and EXEC record types, which makes "perf report" lose
track of symbols when a process renames itself.

With this fix (suggested by Stephane Eranian), a COMM (rename)
no longer flushes the maps, which is the correct behavior.
An EXEC also no longer flushes the maps, but this doesn't
matter because as new mappings are created (for the executable
and the libraries) the old mappings are automatically removed.
This is not by accident: the functionality is necessary because
DLLs can be explicitly loaded at any time with dlopen(),
possibly on top of existing text, so "perf report" handles
correctly the clobbering of new mappings on top of old ones.

An alternative patch (which I proposed earlier) would be to
introduce a separate PERF_RECORD_EXEC type, but it is a much
larger change (about 300 lines) and is not necessary.

Signed-off-by: Luigi Semenzato <semenzato@...omium.org>
---
 tools/perf/util/thread.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index fb4b7ea..8b3e593 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -39,7 +39,6 @@ int thread__set_comm(struct thread *self, const char *comm)
 	err = self->comm == NULL ? -ENOMEM : 0;
 	if (!err) {
 		self->comm_set = true;
-		map_groups__flush(&self->mg);
 	}
 	return err;
 }
-- 
1.7.7.3

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