perf perl 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

Signed-off-by: Jiri Olsa <[email protected]>
Original-patch-by: Andrew Jones <[email protected]>
Cc: Andrew Jones <[email protected]>
Cc: Corey Ashford <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

1 files changed, 5 insertions, 1 deletions

diff --git a/tools/perf/scripts/perl/rwtop.pl b/tools/perf/scripts/perl/rwtop.pl
index 4bb3ecd33472..8b20787021c1 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;
 }