linux-kernel - [PATCH 1/2] perf scripts: Fix SIGALRM and pipe read race for rwtop

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Date:	Tue,  5 Feb 2013 17:05:50 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Andrew Jones <drjones@...hat.com>,
	David Ahern <dsahern@...il.com>
Subject: [PATCH 1/2] perf scripts: Fix SIGALRM and pipe read race for rwtop

Fixing rwtop script race. The issue is caused by rwtop
script triggering SIGALRM and underneath pipe reading
layer reporting error when interrupted.

Fixing this by setting SA_RESTART for rwtop SIGALRM handler,
which avoids interruption of the pipe reading layer.

The discussion for this issue & fix is here:
https://lkml.org/lkml/2012/9/18/123

Original-patch-by: Andrew Jones <drjones@...hat.com>
Signed-off-by: Jiri Olsa <jolsa@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Andrew Jones <drjones@...hat.com>
Cc: David Ahern <dsahern@...il.com>
---
 tools/perf/scripts/perl/rwtop.pl | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/perf/scripts/perl/rwtop.pl b/tools/perf/scripts/perl/rwtop.pl
index 4bb3ecd..8b20787 100644
--- a/tools/perf/scripts/perl/rwtop.pl
+++ b/tools/perf/scripts/perl/rwtop.pl
@@ -17,6 +17,7 @@ use lib "$ENV{'PERF_EXEC_PATH'}/scripts/perl/Perf-Trace-Util/lib";
 use lib "./Perf-Trace-Util/lib";
 use Perf::Trace::Core;
 use Perf::Trace::Util;
+use POSIX qw/SIGALRM SA_RESTART/;
 
 my $default_interval = 3;
 my $nlines = 20;
@@ -90,7 +91,10 @@ sub syscalls::sys_enter_write
 
 sub trace_begin
 {
-    $SIG{ALRM} = \&set_print_pending;
+    my $sa = POSIX::SigAction->new(\&set_print_pending);
+    $sa->flags(SA_RESTART);
+    $sa->safe(1);
+    POSIX::sigaction(SIGALRM, $sa) or die "Can't set SIGALRM handler: $!\n";
     alarm 1;
 }
 
-- 
1.7.11.7

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