[ 40/56] tracing: Prevent buffer overwrite disabled for latency tracers

Greg Kroah-Hartman
2013-04-02T22:56:15Z

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

commit 613f04a0f51e6e68ac6fe571ab79da3c0a5eb4da upstream.

The latency tracers require the buffers to be in overwrite mode,
otherwise they get screwed up. Force the buffers to stay in overwrite
mode when latency tracers are enabled.

Added a flag_changed() method to the tracer structure to allow
the tracers to see what flags are being changed, and also be able
to prevent the change from happing.

[Backported for 3.4-stable. Re-added current_trace NULL checks; removed
allocated_snapshot field; adapted to tracing_trace_options_write without
trace_set_options.]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Lingzhu Xiang <lxiang@redhat.com>
Reviewed-by: CAI Qian <caiqian@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/trace/trace.c | 35 +++++++++++++++++++++++++++++------
kernel/trace/trace.h | 7 +++++++
kernel/trace/trace_irqsoff.c | 19 ++++++++++++++-----
kernel/trace/trace_sched_wakeup.c | 18 +++++++++++++-----
4 files changed, 63 insertions(+), 16 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2527,11 +2527,25 @@ static int set_tracer_option(struct trac
return -EINVAL;
}

-static void set_tracer_flags(unsigned int mask, int enabled)
+/* Some tracers require overwrite to stay enabled */
+int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set)
+{
+ if (tracer->enabled && (mask & TRACE_ITER_OVERWRITE) && !set)
+ return -1;
+
+ return 0;
+}
+
+int set_tracer_flag(unsigned int mask, int enabled)
{
/* do nothing if flag is already set */
if (!!(trace_flags & mask) == !!enabled)
- return;
+ return 0;
+
+ /* Give the tracer a chance to approve the change */
+ if (current_trace->flag_changed)
+ if (current_trace->flag_changed(current_trace, mask, !!enabled))
+ return -EINVAL;

if (enabled)
trace_flags |= mask;
@@ -2543,6 +2557,8 @@ static void set_tracer_flags(unsigned in

if (mask == TRACE_ITER_OVERWRITE)
ring_buffer_change_overwrite(global_trace.buffer, enabled);
+
+ return 0;
}

static ssize_t
@@ -2552,7 +2568,7 @@ tracing_trace_options_write(struct file
char buf[64];
char *cmp;
int neg = 0;
- int ret = 0;
+ int ret = -ENODEV;
int i;

if (cnt >= sizeof(buf))
@@ -2573,7 +2589,7 @@ tracing_trace_options_write(struct file

for (i = 0; trace_options[i]; i++) {
if (strcmp(cmp, trace_options[i]) == 0) {
- set_tracer_flags(1 << i, !neg);
+ ret = set_tracer_flag(1 << i, !neg);
break;
}
}
@@ -2584,7 +2600,7 @@ tracing_trace_options_write(struct file

mutex_unlock(&trace_types_lock);

- if (ret)
+ if (ret < 0)
return ret;

*ppos += cnt;
@@ -2883,6 +2899,9 @@ static int tracing_set_tracer(const char
goto out;

trace_branch_disable();
+
+ current_trace->enabled = false;
+
if (current_trace && current_trace->reset)
current_trace->reset(tr);
if (current_trace && current_trace->use_max_tr) {
@@ -2912,6 +2931,7 @@ static int tracing_set_tracer(const char
goto out;
}

+ current_trace->enabled = true;
trace_branch_enable(tr);
out:
mutex_unlock(&trace_types_lock);
@@ -4184,9 +4204,12 @@ trace_options_core_write(struct file *fi
return -EINVAL;

mutex_lock(&trace_types_lock);
- set_tracer_flags(1 << index, val);
+ ret = set_tracer_flag(1 << index, val);
mutex_unlock(&trace_types_lock);

+ if (ret < 0)
+ return ret;
+
*ppos += cnt;

return cnt;
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -271,10 +271,14 @@ struct tracer {
enum print_line_t (*print_line)(struct trace_iterator *iter);
/* If you handled the flag setting, return 0 */
int (*set_flag)(u32 old_flags, u32 bit, int set);
+ /* Return 0 if OK with change, else return non-zero */
+ int (*flag_changed)(struct tracer *tracer,
+ u32 mask, int set);
struct tracer *next;
struct tracer_flags *flags;
int print_max;
int use_max_tr;
+ bool enabled;
};

@@ -776,6 +780,9 @@ extern struct list_head ftrace_events;
extern const char *__start___trace_bprintk_fmt[];
extern const char *__stop___trace_bprintk_fmt[];

+int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set);
+int set_tracer_flag(unsigned int mask, int enabled);
+
#undef FTRACE_ENTRY
#define FTRACE_ENTRY(call, struct_name, id, tstruct, print) \
extern struct ftrace_event_call \
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -32,7 +32,7 @@ enum {

static int trace_type __read_mostly;

-static int save_lat_flag;
+static int save_flags;

static void stop_irqsoff_tracer(struct trace_array *tr, int graph);
static int start_irqsoff_tracer(struct trace_array *tr, int graph);
@@ -544,8 +544,11 @@ static void stop_irqsoff_tracer(struct t

static void __irqsoff_tracer_init(struct trace_array *tr)
{
- save_lat_flag = trace_flags & TRACE_ITER_LATENCY_FMT;
- trace_flags |= TRACE_ITER_LATENCY_FMT;
+ save_flags = trace_flags;
+
+ /* non overwrite screws up the latency tracers */
+ set_tracer_flag(TRACE_ITER_OVERWRITE, 1);
+ set_tracer_flag(TRACE_ITER_LATENCY_FMT, 1);

tracing_max_latency = 0;
irqsoff_trace = tr;
@@ -559,10 +562,13 @@ static void __irqsoff_tracer_init(struct

static void irqsoff_tracer_reset(struct trace_array *tr)
{
+ int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
+ int overwrite_flag = save_flags & TRACE_ITER_OVERWRITE;
+
stop_irqsoff_tracer(tr, is_graph());

- if (!save_lat_flag)
- trace_flags &= ~TRACE_ITER_LATENCY_FMT;
+ set_tracer_flag(TRACE_ITER_LATENCY_FMT, lat_flag);
+ set_tracer_flag(TRACE_ITER_OVERWRITE, overwrite_flag);
}

static void irqsoff_tracer_start(struct trace_array *tr)
@@ -595,6 +601,7 @@ static struct tracer irqsoff_tracer __re
.print_line = irqsoff_print_line,
.flags = &tracer_flags,
.set_flag = irqsoff_set_flag,
+ .flag_changed = trace_keep_overwrite,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_irqsoff,
#endif
@@ -628,6 +635,7 @@ static struct tracer preemptoff_tracer _
.print_line = irqsoff_print_line,
.flags = &tracer_flags,
.set_flag = irqsoff_set_flag,
+ .flag_changed = trace_keep_overwrite,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_preemptoff,
#endif
@@ -663,6 +671,7 @@ static struct tracer preemptirqsoff_trac
.print_line = irqsoff_print_line,
.flags = &tracer_flags,
.set_flag = irqsoff_set_flag,
+ .flag_changed = trace_keep_overwrite,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_preemptirqsoff,
#endif
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -36,7 +36,7 @@ static void __wakeup_reset(struct trace_
static int wakeup_graph_entry(struct ftrace_graph_ent *trace);
static void wakeup_graph_return(struct ftrace_graph_ret *trace);

-static int save_lat_flag;
+static int save_flags;

#define TRACE_DISPLAY_GRAPH 1

@@ -526,8 +526,11 @@ static void stop_wakeup_tracer(struct tr

static int __wakeup_tracer_init(struct trace_array *tr)
{
- save_lat_flag = trace_flags & TRACE_ITER_LATENCY_FMT;
- trace_flags |= TRACE_ITER_LATENCY_FMT;
+ save_flags = trace_flags;
+
+ /* non overwrite screws up the latency tracers */
+ set_tracer_flag(TRACE_ITER_OVERWRITE, 1);
+ set_tracer_flag(TRACE_ITER_LATENCY_FMT, 1);

tracing_max_latency = 0;
wakeup_trace = tr;
@@ -549,12 +552,15 @@ static int wakeup_rt_tracer_init(struct

static void wakeup_tracer_reset(struct trace_array *tr)
{
+ int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
+ int overwrite_flag = save_flags & TRACE_ITER_OVERWRITE;
+
stop_wakeup_tracer(tr);
/* make sure we put back any tasks we are tracing */
wakeup_reset(tr);

- if (!save_lat_flag)
- trace_flags &= ~TRACE_ITER_LATENCY_FMT;
+ set_tracer_flag(TRACE_ITER_LATENCY_FMT, lat_flag);
+ set_tracer_flag(TRACE_ITER_OVERWRITE, overwrite_flag);
}

static void wakeup_tracer_start(struct trace_array *tr)
@@ -580,6 +586,7 @@ static struct tracer wakeup_tracer __rea
.print_line = wakeup_print_line,
.flags = &tracer_flags,
.set_flag = wakeup_set_flag,
+ .flag_changed = trace_keep_overwrite,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_wakeup,
#endif
@@ -601,6 +608,7 @@ static struct tracer wakeup_rt_tracer __
.print_line = wakeup_print_line,
.flags = &tracer_flags,
.set_flag = wakeup_set_flag,
+ .flag_changed = trace_keep_overwrite,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_wakeup,
#endif