Ftrace has a snapshot feature available from kernel space and
latency tracers (e.g. irqsoff) are using it. This patch enables
user applictions to take a snapshot via debugfs.
Add following two debugfs files in "tracing" directory.
snapshot:
This is used to take a snapshot and to read the output of the
snapshot.
# echo 1 > snapshot
# cat snapshot
snapshot_allocate:
Echoing 1 to the "snapshot" allocates the max_tr buffer if
it is not allocated. So taking a snapshot may delay or fail
beacuse of memory allocation. To avoid that, this file
provides a mean to pre-allocate (or free) the max_tr buffer.
# echo 1 > snapshot_allocate
[...]
# echo 1 > snapshot
Signed-off-by: Hiraku Toyooka <hiraku.toyooka...@hitachi.com>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Jiri Olsa <jo...@redhat.com>
Cc: Li Zefan <l...@cn.fujitsu.com>
Cc: linux-kernel@vger.kernel.org
---
include/linux/ftrace_event.h | 3 +
kernel/trace/Kconfig | 11 ++
kernel/trace/trace.c | 190 +++++++++++++++++++++++++++++++++++++++---
kernel/trace/trace.h | 1
4 files changed, 193 insertions(+), 12 deletions(-)
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 642928c..8c32c6e 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -84,6 +84,9 @@ struct trace_iterator {
long idx;
cpumask_var_t started;
+
+ /* it's true when current open file is snapshot */
+ bool snapshot;
};
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 4cea4f4..73d56d5 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -102,6 +102,17 @@ config RING_BUFFER_ALLOW_SWAP
Allow the use of ring_buffer_swap_cpu.
Adds a very slight overhead to tracing when enabled.
+config TRACER_SNAPSHOT
+ bool
+ default y
+ select TRACER_MAX_TRACE
+ help
+ Allow tracing users to take snapshot of the current buffer using the
+ ftrace interface, e.g.:
+
+ echo 1 > /sys/kernel/debug/tracing/snapshot
+ cat snapshot
+
# All tracer options should select GENERIC_TRACER. For those options that are
# enabled by all tracers (context switch and event tracer) they select TRACING.
# This allows those options to appear when no other tracer is selected. But the
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1e599e6..dac5733 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -699,7 +699,7 @@ update_max_tr(struct trace_array *tr, struct task_struct
*tsk, int cpu)
return;
WARN_ON_ONCE(!irqs_disabled());
- if (!current_trace->use_max_tr) {
+ if (!current_trace->allocated_snapshot) {
WARN_ON_ONCE(1);
return;
}
@@ -729,7 +729,7 @@ update_max_tr_single(struct trace_array *tr, struct
task_struct *tsk, int cpu)
return;
WARN_ON_ONCE(!irqs_disabled());
- if (!current_trace->use_max_tr) {
+ if (!current_trace->allocated_snapshot) {
WARN_ON_ONCE(1);
return;
}
@@ -1902,7 +1902,8 @@ static void *s_start(struct seq_file *m, loff_t *pos)
}
mutex_unlock(&trace_types_lock);
- atomic_inc(&trace_record_cmdline_disabled);
+ if (!iter->snapshot)
+ atomic_inc(&trace_record_cmdline_disabled);
if (*pos != iter->pos) {
iter->ent = NULL;
@@ -1941,7 +1942,8 @@ static void s_stop(struct seq_file *m, void *p)
{
struct trace_iterator *iter = m->private;
- atomic_dec(&trace_record_cmdline_disabled);
+ if (!iter->snapshot)
+ atomic_dec(&trace_record_cmdline_disabled);
trace_access_unlock(iter->cpu_file);
trace_event_read_unlock();
}
@@ -2375,7 +2377,7 @@ static const struct seq_operations tracer_seq_ops = {
};
static struct trace_iterator *
-__tracing_open(struct inode *inode, struct file *file)
+__tracing_open(struct inode *inode, struct file *file, int snapshot)
{
long cpu_file = (long) inode->i_private;
struct trace_iterator *iter;
@@ -2408,10 +2410,11 @@ __tracing_open(struct inode *inode, struct file *file)
if (!zalloc_cpumask_var(&iter->started, GFP_KERNEL))
goto fail;
- if (current_trace && current_trace->print_max)
+ if ((current_trace && current_trace->print_max) || snapshot)
iter->tr = &max_tr;
else
iter->tr = &global_trace;
+ iter->snapshot = !!snapshot;
iter->pos = -1;
mutex_init(&iter->mutex);
iter->cpu_file = cpu_file;
@@ -2424,8 +2427,9 @@ __tracing_open(struct inode *inode, struct file *file)
if (ring_buffer_overruns(iter->tr->buffer))
iter->iter_flags |= TRACE_FILE_ANNOTATE;
- /* stop the trace while dumping */
- tracing_stop();
+ /* stop the trace while dumping if we are not opening "snapshot" */
+ if (!iter->snapshot)
+ tracing_stop();
if (iter->cpu_file == TRACE_PIPE_ALL_CPU) {
for_each_tracing_cpu(cpu) {
@@ -2488,8 +2492,9 @@ static int tracing_release(struct inode *inode, struct
file *file)
if (iter->trace && iter->trace->close)
iter->trace->close(iter);
- /* reenable tracing if it was previously enabled */
- tracing_start();
+ if (!iter->snapshot)
+ /* reenable tracing if it was previously enabled */
+ tracing_start();
mutex_unlock(&trace_types_lock);
mutex_destroy(&iter->mutex);
@@ -2517,7 +2522,7 @@ static int tracing_open(struct inode *inode, struct file
*file)
}
if (file->f_mode & FMODE_READ) {
- iter = __tracing_open(inode, file);
+ iter = __tracing_open(inode, file, 0);
if (IS_ERR(iter))
ret = PTR_ERR(iter);
else if (trace_flags & TRACE_ITER_LATENCY_FMT)
@@ -3185,7 +3190,8 @@ static int tracing_set_tracer(const char *buf)
trace_branch_disable();
if (current_trace && current_trace->reset)
current_trace->reset(tr);
- if (current_trace && current_trace->use_max_tr) {
+ if (current_trace && current_trace->allocated_snapshot) {
+ tracing_reset_online_cpus(&max_tr);
/*
* We don't free the ring buffer. instead, resize it because
* The max_tr ring buffer has some state (e.g. ring->clock) and
@@ -3193,6 +3199,7 @@ static int tracing_set_tracer(const char *buf)
*/
ring_buffer_resize(max_tr.buffer, 1, RING_BUFFER_ALL_CPUS);
set_buffer_entries(&max_tr, 1);
+ current_trace->allocated_snapshot = false;
}
destroy_trace_option_files(topts);
@@ -3205,6 +3212,7 @@ static int tracing_set_tracer(const char *buf)
RING_BUFFER_ALL_CPUS);
if (ret < 0)
goto out;
+ t->allocated_snapshot = true;
}
if (t->init) {
@@ -4028,6 +4036,139 @@ static int tracing_clock_open(struct inode *inode,
struct file *file)
return single_open(file, tracing_clock_show, NULL);
}
+#ifdef CONFIG_TRACER_SNAPSHOT
+static int tracing_snapshot_open(struct inode *inode, struct file *file)
+{
+ struct trace_iterator *iter;
+ int ret = 0;
+
+ if (file->f_mode & FMODE_READ) {
+ iter = __tracing_open(inode, file, 1);
+ if (IS_ERR(iter))
+ ret = PTR_ERR(iter);
+ }
+ return ret;
+}
+
+static ssize_t tracing_snapshot_read(struct file *filp, char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ ssize_t ret = 0;
+
+ mutex_lock(&trace_types_lock);
+ if (current_trace && current_trace->use_max_tr)
+ ret = -EBUSY;
+ mutex_unlock(&trace_types_lock);
+ if (ret < 0)
+ return ret;
+
+ ret = seq_read(filp, ubuf, cnt, ppos);
+
+ return ret;
+}
+
+static ssize_t
+tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
+ loff_t *ppos)
+{
+ unsigned long val = 0;
+ int ret;
+
+ ret = tracing_update_buffers();
+ if (ret < 0)
+ return ret;
+
+ ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+ if (ret)
+ return ret;
+
+ mutex_lock(&trace_types_lock);
+
+ if (current_trace->use_max_tr) {
+ ret = -EBUSY;
+ goto out;
+ }
+
+ if (!current_trace->allocated_snapshot) {
+ /* allocate spare buffer for snapshot */
+ ret = resize_buffer_even(&max_tr, &global_trace,
+ RING_BUFFER_ALL_CPUS);
+ if (ret < 0)
+ goto out;
+ current_trace->allocated_snapshot = true;
+ }
+
+ if (val) {
+ local_irq_disable();
+ update_max_tr(&global_trace, current, smp_processor_id());
+ local_irq_enable();
+ } else
+ tracing_reset_online_cpus(&max_tr);
+
+ *ppos += cnt;
+ ret = cnt;
+out:
+ mutex_unlock(&trace_types_lock);
+ return ret;
+}
+
+static ssize_t
+tracing_snapshot_allocate_read(struct file *filp, char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[64];
+ int r;
+
+ r = sprintf(buf, "%d\n", current_trace->allocated_snapshot);
+ return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
+}
+
+static ssize_t
+tracing_snapshot_allocate_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ unsigned long val;
+ int ret;
+
+ ret = tracing_update_buffers();
+ if (ret < 0)
+ return ret;
+
+ ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
+ if (ret)
+ return ret;
+
+ mutex_lock(&trace_types_lock);
+
+ if (current_trace->use_max_tr) {
+ ret = -EBUSY;
+ goto out;
+ }
+
+ if (current_trace->allocated_snapshot == !val) {
+ if (val) {
+ /* allocate spare buffer for snapshot */
+ ret = resize_buffer_even(&max_tr, &global_trace,
+ RING_BUFFER_ALL_CPUS);
+ if (ret < 0)
+ goto out;
+ } else {
+ tracing_reset_online_cpus(&max_tr);
+ ring_buffer_resize(max_tr.buffer, 1,
+ RING_BUFFER_ALL_CPUS);
+ set_buffer_entries(&max_tr, 1);
+ }
+ current_trace->allocated_snapshot = !!val;
+ }
+
+ *ppos += cnt;
+ ret = cnt;
+out:
+ mutex_unlock(&trace_types_lock);
+ return ret;
+}
+#endif /* CONFIG_TRACER_SNAPSHOT */
+
static const struct file_operations tracing_max_lat_fops = {
.open = tracing_open_generic,
.read = tracing_max_lat_read,
@@ -4091,6 +4232,23 @@ static const struct file_operations trace_clock_fops = {
.write = tracing_clock_write,
};
+#ifdef CONFIG_TRACER_SNAPSHOT
+static const struct file_operations snapshot_fops = {
+ .open = tracing_snapshot_open,
+ .read = tracing_snapshot_read,
+ .write = tracing_snapshot_write,
+ .llseek = tracing_seek,
+ .release = tracing_release,
+};
+
+static const struct file_operations snapshot_allocate_fops = {
+ .open = tracing_open_generic,
+ .read = tracing_snapshot_allocate_read,
+ .write = tracing_snapshot_allocate_write,
+ .llseek = generic_file_llseek,
+};
+#endif /* CONFIG_TRACER_SNAPSHOT */
+
struct ftrace_buffer_info {
struct trace_array *tr;
void *spare;
@@ -4877,6 +5035,14 @@ static __init int tracer_init_debugfs(void)
&ftrace_update_tot_cnt, &tracing_dyn_info_fops);
#endif
+#ifdef CONFIG_TRACER_SNAPSHOT
+ trace_create_file("snapshot", 0644, d_tracer,
+ (void *) TRACE_PIPE_ALL_CPU, &snapshot_fops);
+
+ trace_create_file("snapshot_allocate", 0644, d_tracer,
+ NULL, &snapshot_allocate_fops);
+#endif
+
create_trace_options_dir();
for_each_tracing_cpu(cpu)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 0eb6a1a..66a8631 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -287,6 +287,7 @@ struct tracer {
struct tracer_flags *flags;
bool print_max;
bool use_max_tr;
+ bool allocated_snapshot;
};
--
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