[PATCH 2/3] tracing: protect reader of cmdline output

Steven Rostedt
2009-03-17T03:50:56Z

[-- Attachment #1: 0002-tracing-protect-reader-of-cmdline-output.patch --]
[-- Type: text/plain, Size: 6376 bytes --]

From: Steven Rostedt <srostedt@redhat.com>

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>
---
kernel/trace/blktrace.c | 23 ++++++++++++++++++-----
kernel/trace/trace.c | 20 ++++++++++++--------
kernel/trace/trace.h | 2 +-
kernel/trace/trace_functions_graph.c | 12 ++++++------
kernel/trace/trace_output.c | 18 ++++++++++++------
5 files changed, 49 insertions(+), 26 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 1f32e4e..b171778 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -1027,7 +1027,9 @@ static int blk_log_action_seq(struct trace_seq *s, const struct blk_io_trace *t,

static int blk_log_generic(struct trace_seq *s, const struct trace_entry *ent)
{
- const char *cmd = trace_find_cmdline(ent->pid);
+ char cmd[TASK_COMM_LEN];
+
+ trace_find_cmdline(ent->pid, cmd);

if (t_sec(ent))
return trace_seq_printf(s, "%llu + %u [%s]\n",
@@ -1057,19 +1059,30 @@ static int blk_log_remap(struct trace_seq *s, const struct trace_entry *ent)

static int blk_log_plug(struct trace_seq *s, const struct trace_entry *ent)
{
- return trace_seq_printf(s, "[%s]\n", trace_find_cmdline(ent->pid));
+ char cmd[TASK_COMM_LEN];
+
+ trace_find_cmdline(ent->pid, cmd);
+
+ return trace_seq_printf(s, "[%s]\n", cmd);
}

static int blk_log_unplug(struct trace_seq *s, const struct trace_entry *ent)
{
- return trace_seq_printf(s, "[%s] %llu\n", trace_find_cmdline(ent->pid),
- get_pdu_int(ent));
+ char cmd[TASK_COMM_LEN];
+
+ trace_find_cmdline(ent->pid, cmd);
+
+ return trace_seq_printf(s, "[%s] %llu\n", cmd, get_pdu_int(ent));
}

static int blk_log_split(struct trace_seq *s, const struct trace_entry *ent)
{
+ char cmd[TASK_COMM_LEN];
+
+ trace_find_cmdline(ent->pid, cmd);
+
return trace_seq_printf(s, "%llu / %llu [%s]\n", t_sector(ent),
- get_pdu_int(ent), trace_find_cmdline(ent->pid));
+ get_pdu_int(ent), cmd);
}

/*
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index efe3202..2796bd2 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -770,25 +770,29 @@ static void trace_save_cmdline(struct task_struct *tsk)
__raw_spin_unlock(&trace_cmdline_lock);
}

-char *trace_find_cmdline(int pid)
+void trace_find_cmdline(int pid, char comm[])
{
- char *cmdline = "<...>";
unsigned map;

- if (!pid)
- return "<idle>";
+ if (!pid) {
+ strcpy(comm, "<idle>");
+ return;
+ }

- if (pid > PID_MAX_DEFAULT)
- goto out;
+ if (pid > PID_MAX_DEFAULT) {
+ strcpy(comm, "<...>");
+ return;
+ }

+ __raw_spin_lock(&trace_cmdline_lock);
map = map_pid_to_cmdline[pid];
if (map >= SAVED_CMDLINES)
goto out;

- cmdline = saved_cmdlines[map];
+ strcpy(comm, saved_cmdlines[map]);

out:
- return cmdline;
+ __raw_spin_unlock(&trace_cmdline_lock);
}

void tracing_record_cmdline(struct task_struct *tsk)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 56ce34d..b0ecad8 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -547,7 +547,7 @@ struct tracer_switch_ops {
};
#endif /* CONFIG_CONTEXT_SWITCH_TRACER */

-extern char *trace_find_cmdline(int pid);
+extern void trace_find_cmdline(int pid, char comm[]);

#ifdef CONFIG_DYNAMIC_FTRACE
extern unsigned long ftrace_update_tot_cnt;
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);

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 @@ static int
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 @@ int trace_print_context(struct trace_iterator *iter)
{
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 @@ int trace_print_lat_context(struct trace_iterator *iter)
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 @@ static enum print_line_t trace_ctxwake_print(struct trace_iterator *iter,
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,
--
1.6.2

--