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tracing: Move locking of trace_cmdline_lock into start/stop seq calls 

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: 42584c81c5 tracing: Have saved_cmdlines use the seq_read infrastructure
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Red Hat) 2014-05-30 10:49:46 -04:00 committed by Steven Rostedt
parent 379cfdac37
commit 4c27e756bc
1 changed files with 15 additions and 4 deletions
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19
kernel/trace/trace.c
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@ -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;
}