[for-next][PATCH 7/7] tracing: Move locking of trace_cmdline_lock into start/stop seq calls

Steven Rostedt
2014-05-31T01:40:08Z

[-- Attachment #1: 0006-tracing-Move-locking-of-trace_cmdline_lock-into-star.patch --]
[-- Type: text/plain, Size: 2332 bytes --]

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

With the conversion of the saved_cmdlines output to use seq_read, there
is now a race between accessing the values of the saved_cmdlines and
the writing to them. The trace_cmdline_lock needs to be taken at
the start and stop of the seq calls.

A new __trace_find_cmdline() call is created to allow for the look up
to happen without taking the lock.

Fixes: 42584c81c5ad tracing: Have saved_cmdlines use the seq_read infrastructure
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 22a902e2ded9..626dbfde5d56 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1484,7 +1484,7 @@ static int trace_save_cmdline(struct task_struct *tsk)
return 1;
}

-void trace_find_cmdline(int pid, char comm[])
+static void __trace_find_cmdline(int pid, char comm[])
{
unsigned map;

@@ -1503,13 +1503,19 @@ void trace_find_cmdline(int pid, char comm[])
return;
}

- preempt_disable();
- arch_spin_lock(&trace_cmdline_lock);
map = map_pid_to_cmdline[pid];
if (map != NO_CMDLINE_MAP)
strcpy(comm, saved_cmdlines[map]);
else
strcpy(comm, "<...>");
+}
+
+void trace_find_cmdline(int pid, char comm[])
+{
+ preempt_disable();
+ arch_spin_lock(&trace_cmdline_lock);
+
+ __trace_find_cmdline(pid, comm);

arch_spin_unlock(&trace_cmdline_lock);
preempt_enable();
@@ -3724,6 +3730,9 @@ static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
void *v;
loff_t l = 0;

+ preempt_disable();
+ arch_spin_lock(&trace_cmdline_lock);
+
v = &map_cmdline_to_pid[0];
while (l <= *pos) {
v = saved_cmdlines_next(m, v, &l);
@@ -3736,6 +3745,8 @@ static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)

static void saved_cmdlines_stop(struct seq_file *m, void *v)
{
+ arch_spin_unlock(&trace_cmdline_lock);
+ preempt_enable();
}

static int saved_cmdlines_show(struct seq_file *m, void *v)
@@ -3743,7 +3754,7 @@ static int saved_cmdlines_show(struct seq_file *m, void *v)
char buf[TASK_COMM_LEN];
unsigned int *pid = v;

- trace_find_cmdline(*pid, buf);
+ __trace_find_cmdline(*pid, buf);
seq_printf(m, "%d %s\n", *pid, buf);
return 0;
}
--
2.0.0.rc2