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 4c38860..6004cca 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);