tracing: protect reader of cmdline output

Impact: fix to one cause of incorrect comm outputs in trace

The spinlock only protected the creation of a comm <=> pid pair.
But it was possible that a reader could look up a pid, and get the
wrong comm because it had no locking.

This also required changing trace_find_cmdline to copy the comm cache
and not just send back a pointer to it.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 4c388607ed67..6004ccac2dd7 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -190,15 +190,15 @@ print_graph_cpu(struct trace_seq *s, int cpu)
 static enum print_line_t
 print_graph_proc(struct trace_seq *s, pid_t pid)
 {
-        int i;
-        int ret;
-        int len;
-        char comm[8];
-        int spaces = 0;
+        char comm[TASK_COMM_LEN];
         /* sign + log10(MAX_INT) + '\0' */
         char pid_str[11];
+        int spaces = 0;
+        int ret;
+        int len;
+        int i;
 
-        strncpy(comm, trace_find_cmdline(pid), 7);
+        trace_find_cmdline(pid, comm);
         comm[7] = '\0';
         sprintf(pid_str, "%d", pid);