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>
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index ea9d3b4..6a4c9de 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -309,9 +309,9 @@
lat_print_generic(struct trace_seq *s, struct trace_entry *entry, int cpu)
{
int hardirq, softirq;
- char *comm;
+ char comm[TASK_COMM_LEN];
- comm = trace_find_cmdline(entry->pid);
+ trace_find_cmdline(entry->pid, comm);
hardirq = entry->flags & TRACE_FLAG_HARDIRQ;
softirq = entry->flags & TRACE_FLAG_SOFTIRQ;
@@ -346,10 +346,12 @@
{
struct trace_seq *s = &iter->seq;
struct trace_entry *entry = iter->ent;
- char *comm = trace_find_cmdline(entry->pid);
unsigned long long t = ns2usecs(iter->ts);
unsigned long usec_rem = do_div(t, USEC_PER_SEC);
unsigned long secs = (unsigned long)t;
+ char comm[TASK_COMM_LEN];
+
+ trace_find_cmdline(entry->pid, comm);
return trace_seq_printf(s, "%16s-%-5d [%03d] %5lu.%06lu: ",
comm, entry->pid, iter->cpu, secs, usec_rem);
@@ -372,7 +374,10 @@
rel_usecs = ns2usecs(next_ts - iter->ts);
if (verbose) {
- char *comm = trace_find_cmdline(entry->pid);
+ char comm[TASK_COMM_LEN];
+
+ trace_find_cmdline(entry->pid, comm);
+
ret = trace_seq_printf(s, "%16s %5d %3d %d %08x %08lx [%08lx]"
" %ld.%03ldms (+%ld.%03ldms): ", comm,
entry->pid, iter->cpu, entry->flags,
@@ -577,14 +582,15 @@
char *delim)
{
struct ctx_switch_entry *field;
- char *comm;
+ char comm[TASK_COMM_LEN];
int S, T;
+
trace_assign_type(field, iter->ent);
T = task_state_char(field->next_state);
S = task_state_char(field->prev_state);
- comm = trace_find_cmdline(field->next_pid);
+ trace_find_cmdline(field->next_pid, comm);
if (!trace_seq_printf(&iter->seq,
" %5d:%3d:%c %s [%03d] %5d:%3d:%c %s\n",
field->prev_pid,
