[tip:tracing/tasks] tracing: fix command line to pid reverse map

Carsten Emde
2009-03-18T09:20:53Z

Commit-ID: a635cf0497342978d417cae19d4a4823932977ff
Gitweb: http://git.kernel.org/tip/a635cf0497342978d417cae19d4a4823932977ff
Author: Carsten Emde <Carsten.Emde@osadl.org>
AuthorDate: Wed, 18 Mar 2009 09:00:41 +0100
Commit: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 18 Mar 2009 10:10:18 +0100

tracing: fix command line to pid reverse map

Impact: fix command line to pid mapping

map_cmdline_to_pid[] is checked in trace_save_cmdline(), but never
updated. This results in stale pid to command line mappings and the
tracer output will associate the wrong comm string.

Signed-off-by: Carsten Emde <Carsten.Emde@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
kernel/trace/trace.c | 16 +++++++++++-----
1 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 06c69a2..305c562 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -738,8 +738,7 @@ void trace_stop_cmdline_recording(void);

static void trace_save_cmdline(struct task_struct *tsk)
{
- unsigned map;
- unsigned idx;
+ unsigned pid, idx;

if (!tsk->pid || unlikely(tsk->pid > PID_MAX_DEFAULT))
return;
@@ -757,10 +756,17 @@ static void trace_save_cmdline(struct task_struct *tsk)
if (idx == NO_CMDLINE_MAP) {
idx = (cmdline_idx + 1) % SAVED_CMDLINES;

- map = map_cmdline_to_pid[idx];
- if (map != NO_CMDLINE_MAP)
- map_pid_to_cmdline[map] = NO_CMDLINE_MAP;
+ /*
+ * Check whether the cmdline buffer at idx has a pid
+ * mapped. We are going to overwrite that entry so we
+ * need to clear the map_pid_to_cmdline. Otherwise we
+ * would read the new comm for the old pid.
+ */
+ pid = map_cmdline_to_pid[idx];
+ if (pid != NO_CMDLINE_MAP)
+ map_pid_to_cmdline[pid] = NO_CMDLINE_MAP;

+ map_cmdline_to_pid[idx] = tsk->pid;
map_pid_to_cmdline[tsk->pid] = idx;

cmdline_idx = idx;