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Subject[PATCH 4/4] ftrace: Add set_graph_notrace filter
Date
From: Namhyung Kim <namhyung.kim@lge.com>

The set_graph_notrace filter is analogous to set_ftrace_notrace and
can be used for eliminating uninteresting part of function graph trace
output. It also works with set_graph_function nicely.

# cd /sys/kernel/debug/tracing/
# echo do_page_fault > set_graph_function
# perf ftrace live true
2) | do_page_fault() {
2) | __do_page_fault() {
2) 0.381 us | down_read_trylock();
2) 0.055 us | __might_sleep();
2) 0.696 us | find_vma();
2) | handle_mm_fault() {
2) | handle_pte_fault() {
2) | __do_fault() {
2) | filemap_fault() {
2) | find_get_page() {
2) 0.033 us | __rcu_read_lock();
2) 0.035 us | __rcu_read_unlock();
2) 1.696 us | }
2) 0.031 us | __might_sleep();
2) 2.831 us | }
2) | _raw_spin_lock() {
2) 0.046 us | add_preempt_count();
2) 0.841 us | }
2) 0.033 us | page_add_file_rmap();
2) | _raw_spin_unlock() {
2) 0.057 us | sub_preempt_count();
2) 0.568 us | }
2) | unlock_page() {
2) 0.084 us | page_waitqueue();
2) 0.126 us | __wake_up_bit();
2) 1.117 us | }
2) 7.729 us | }
2) 8.397 us | }
2) 8.956 us | }
2) 0.085 us | up_read();
2) + 12.745 us | }
2) + 13.401 us | }
...

# echo handle_mm_fault > set_graph_notrace
# perf ftrace live true
1) | do_page_fault() {
1) | __do_page_fault() {
1) 0.205 us | down_read_trylock();
1) 0.041 us | __might_sleep();
1) 0.344 us | find_vma();
1) 0.069 us | up_read();
1) 4.692 us | }
1) 5.311 us | }
...

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
include/linux/ftrace.h | 1 +
kernel/trace/ftrace.c | 33 +++++++++++++++++++++
kernel/trace/trace.h | 22 ++++++++++++++
kernel/trace/trace_functions_graph.c | 56 ++++++++++++++++++++++++++++++++++--
4 files changed, 109 insertions(+), 3 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 9f15c0064c50..ec85d48619e1 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -721,6 +721,7 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
extern char __irqentry_text_start[];
extern char __irqentry_text_end[];

+#define FTRACE_NOTRACE_DEPTH 65536
#define FTRACE_RETFUNC_DEPTH 50
#define FTRACE_RETSTACK_ALLOC_SIZE 32
extern int register_ftrace_graph(trace_func_graph_ret_t retfunc,
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 26a229ab0c19..44e826a79665 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3776,7 +3776,9 @@ static const struct file_operations ftrace_notrace_fops = {
static DEFINE_MUTEX(graph_lock);

int ftrace_graph_count;
+int ftrace_graph_notrace_count;
unsigned long ftrace_graph_funcs[FTRACE_GRAPH_MAX_FUNCS] __read_mostly;
+unsigned long ftrace_graph_notrace_funcs[FTRACE_GRAPH_MAX_FUNCS] __read_mostly;

struct ftrace_graph_data {
unsigned long *table;
@@ -3891,6 +3893,26 @@ ftrace_graph_open(struct inode *inode, struct file *file)
}

static int
+ftrace_graph_notrace_open(struct inode *inode, struct file *file)
+{
+ struct ftrace_graph_data *fgd;
+
+ if (unlikely(ftrace_disabled))
+ return -ENODEV;
+
+ fgd = kmalloc(sizeof(*fgd), GFP_KERNEL);
+ if (fgd == NULL)
+ return -ENOMEM;
+
+ fgd->table = ftrace_graph_notrace_funcs;
+ fgd->size = FTRACE_GRAPH_MAX_FUNCS;
+ fgd->count = &ftrace_graph_notrace_count;
+ fgd->seq_ops = &ftrace_graph_seq_ops;
+
+ return __ftrace_graph_open(inode, file, fgd);
+}
+
+static int
ftrace_graph_release(struct inode *inode, struct file *file)
{
if (file->f_mode & FMODE_READ) {
@@ -4011,6 +4033,14 @@ static const struct file_operations ftrace_graph_fops = {
.llseek = ftrace_filter_lseek,
.release = ftrace_graph_release,
};
+
+static const struct file_operations ftrace_graph_notrace_fops = {
+ .open = ftrace_graph_notrace_open,
+ .read = seq_read,
+ .write = ftrace_graph_write,
+ .llseek = ftrace_filter_lseek,
+ .release = ftrace_graph_release,
+};
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

static __init int ftrace_init_dyn_debugfs(struct dentry *d_tracer)
@@ -4032,6 +4062,9 @@ static __init int ftrace_init_dyn_debugfs(struct dentry *d_tracer)
trace_create_file("set_graph_function", 0444, d_tracer,
NULL,
&ftrace_graph_fops);
+ trace_create_file("set_graph_notrace", 0444, d_tracer,
+ NULL,
+ &ftrace_graph_notrace_fops);
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

return 0;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 1ea31a7b1890..fec2d75a733f 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -732,6 +732,8 @@ extern void __trace_graph_return(struct trace_array *tr,
#define FTRACE_GRAPH_MAX_FUNCS 32
extern int ftrace_graph_count;
extern unsigned long ftrace_graph_funcs[FTRACE_GRAPH_MAX_FUNCS];
+extern int ftrace_graph_notrace_count;
+extern unsigned long ftrace_graph_notrace_funcs[FTRACE_GRAPH_MAX_FUNCS];

static inline int ftrace_graph_addr(unsigned long addr)
{
@@ -757,11 +759,31 @@ static inline int ftrace_graph_addr(unsigned long addr)

return 0;
}
+
+static inline int ftrace_graph_notrace_addr(unsigned long addr)
+{
+ int i;
+
+ if (!ftrace_graph_notrace_count)
+ return 0;
+
+ for (i = 0; i < ftrace_graph_notrace_count; i++) {
+ if (addr == ftrace_graph_notrace_funcs[i])
+ return 1;
+ }
+
+ return 0;
+}
#else
static inline int ftrace_graph_addr(unsigned long addr)
{
return 1;
}
+
+static inline int ftrace_graph_notrace_addr(unsigned long addr)
+{
+ return 0;
+}
#endif /* CONFIG_DYNAMIC_FTRACE */
#else /* CONFIG_FUNCTION_GRAPH_TRACER */
static inline enum print_line_t
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index b5c09242683d..e08c030b8f38 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -114,16 +114,37 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
return -EBUSY;
}

+ /*
+ * The curr_ret_stack is an index to ftrace return stack of
+ * current task. Its value should be in [0, FTRACE_RETFUNC_
+ * DEPTH) when the function graph tracer is used. To support
+ * filtering out specific functions, it makes the index
+ * negative by subtracting huge value (FTRACE_NOTRACE_DEPTH)
+ * so when it sees a negative index the ftrace will ignore
+ * the record. And the index gets recovered when returning
+ * from the filtered function by adding the FTRACE_NOTRACE_
+ * DEPTH and then it'll continue to record functions normally.
+ *
+ * The curr_ret_stack is initialized to -1 and get increased
+ * in this function. So it can be less than -1 only if it was
+ * filtered out via ftrace_graph_notrace_addr() which can be
+ * set from set_graph_notrace file in debugfs by user.
+ */
+ if (current->curr_ret_stack < -1)
+ return -EBUSY;
+
calltime = trace_clock_local();

index = ++current->curr_ret_stack;
+ if (ftrace_graph_notrace_addr(func))
+ current->curr_ret_stack -= FTRACE_NOTRACE_DEPTH;
barrier();
current->ret_stack[index].ret = ret;
current->ret_stack[index].func = func;
current->ret_stack[index].calltime = calltime;
current->ret_stack[index].subtime = 0;
current->ret_stack[index].fp = frame_pointer;
- *depth = index;
+ *depth = current->curr_ret_stack;

return 0;
}
@@ -137,7 +158,17 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,

index = current->curr_ret_stack;

- if (unlikely(index < 0)) {
+ /*
+ * A negative index here means that it's just returned from a
+ * notrace'd function. Recover index to get an original
+ * return address. See ftrace_push_return_trace().
+ *
+ * TODO: Need to check whether the stack gets corrupted.
+ */
+ if (index < 0)
+ index += FTRACE_NOTRACE_DEPTH;
+
+ if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
ftrace_graph_stop();
WARN_ON(1);
/* Might as well panic, otherwise we have no where to go */
@@ -193,6 +224,15 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
trace.rettime = trace_clock_local();
barrier();
current->curr_ret_stack--;
+ /*
+ * The curr_ret_stack can be less than -1 only if it was
+ * filtered out and it's about to return from the function.
+ * Recover the index and continue to trace normal functions.
+ */
+ if (current->curr_ret_stack < -1) {
+ current->curr_ret_stack += FTRACE_NOTRACE_DEPTH;
+ return ret;
+ }

/*
* The trace should run after decrementing the ret counter
@@ -259,10 +299,20 @@ int trace_graph_entry(struct ftrace_graph_ent *trace)

/* trace it when it is-nested-in or is a function enabled. */
if ((!(trace->depth || ftrace_graph_addr(trace->func)) ||
- ftrace_graph_ignore_irqs()) ||
+ ftrace_graph_ignore_irqs()) || (trace->depth < 0) ||
(max_depth && trace->depth >= max_depth))
return 0;

+ /*
+ * Do not trace a function if it's filtered by set_graph_notrace.
+ * Make the index of ret stack negative to indicate that it should
+ * ignore further functions. But it needs its own ret stack entry
+ * to recover the original index in order to continue tracing after
+ * returning from the function.
+ */
+ if (ftrace_graph_notrace_addr(trace->func))
+ return 1;
+
local_irq_save(flags);
cpu = raw_smp_processor_id();
data = per_cpu_ptr(tr->trace_buffer.data, cpu);
--
1.7.11.7


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