[RFC][PATCH 11/14] function_graph: Convert ret_stack to a series of longs

From: Steven Rostedt
Date: Wed Nov 21 2018 - 20:28:56 EST

From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

In order to make it possible to have multiple callbacks registered with the
function_graph tracer, the retstack needs to be converted from an array of
ftrace_ret_stack structures to an array of longs. This will allow to store
the list of callbacks on the stack for the return side of the functions.

[ Note, this currently breaks architectures that access the ret_stack of a
task to handle unwinding when 'return_to_handler' is on the stack ]

Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
include/linux/sched.h | 2 +-
kernel/trace/fgraph.c | 123 +++++++++++++++++++++++-------------------
2 files changed, 70 insertions(+), 55 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d6183a55e8eb..71a084a300da 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1119,7 +1119,7 @@ struct task_struct {
int curr_ret_depth;

/* Stack of return addresses for return function tracing: */
- struct ftrace_ret_stack *ret_stack;
+ unsigned long *ret_stack;

/* Timestamp for last schedule: */
unsigned long long ftrace_timestamp;
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 9b85638ecded..1389fe39f64c 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -23,6 +23,17 @@
#define ASSIGN_OPS_HASH(opsname, val)
#endif

+#define FGRAPH_RET_SIZE (sizeof(struct ftrace_ret_stack))
+#define FGRAPH_RET_INDEX (ALIGN(FGRAPH_RET_SIZE, sizeof(long)) / sizeof(long))
+#define SHADOW_STACK_SIZE (FTRACE_RETFUNC_DEPTH * FGRAPH_RET_SIZE)
+#define SHADOW_STACK_INDEX \
+ (ALIGN(SHADOW_STACK_SIZE, sizeof(long)) / sizeof(long))
+#define SHADOW_STACK_MAX_INDEX (SHADOW_STACK_INDEX - FGRAPH_RET_INDEX)
+
+#define RET_STACK(t, index) ((struct ftrace_ret_stack *)(&(t)->ret_stack[index]))
+#define RET_STACK_INC(c) ({ c += FGRAPH_RET_INDEX; })
+#define RET_STACK_DEC(c) ({ c -= FGRAPH_RET_INDEX; })
+
static bool kill_ftrace_graph;
int ftrace_graph_active;

@@ -59,6 +70,7 @@ static int
ftrace_push_return_trace(unsigned long ret, unsigned long func,
unsigned long frame_pointer, unsigned long *retp)
{
+ struct ftrace_ret_stack *ret_stack;
unsigned long long calltime;
int index;

@@ -75,23 +87,25 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func,
smp_rmb();

/* The return trace stack is full */
- if (current->curr_ret_stack == FTRACE_RETFUNC_DEPTH - 1) {
+ if (current->curr_ret_stack > SHADOW_STACK_MAX_INDEX) {
atomic_inc(&current->trace_overrun);
return -EBUSY;
}

calltime = trace_clock_local();

- index = ++current->curr_ret_stack;
+ index = current->curr_ret_stack;
+ RET_STACK_INC(current->curr_ret_stack);
+ ret_stack = RET_STACK(current, index);
barrier();
- current->ret_stack[index].ret = ret;
- current->ret_stack[index].func = func;
- current->ret_stack[index].calltime = calltime;
+ ret_stack->ret = ret;
+ ret_stack->func = func;
+ ret_stack->calltime = calltime;
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
- current->ret_stack[index].fp = frame_pointer;
+ ret_stack->fp = frame_pointer;
#endif
#ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
- current->ret_stack[index].retp = retp;
+ ret_stack->retp = retp;
#endif
return 0;
}
@@ -114,7 +128,7 @@ int function_graph_enter(unsigned long ret, unsigned long func,

return 0;
out_ret:
- current->curr_ret_stack--;
+ RET_STACK_DEC(current->curr_ret_stack);
out:
current->curr_ret_depth--;
return -EBUSY;
@@ -125,11 +139,13 @@ static void
ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
unsigned long frame_pointer)
{
+ struct ftrace_ret_stack *ret_stack;
int index;

index = current->curr_ret_stack;
+ RET_STACK_DEC(index);

- if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
+ if (unlikely(index < 0 || index > SHADOW_STACK_MAX_INDEX)) {
ftrace_graph_stop();
WARN_ON(1);
/* Might as well panic, otherwise we have no where to go */
@@ -137,6 +153,7 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
return;
}

+ ret_stack = RET_STACK(current, index);
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
/*
* The arch may choose to record the frame pointer used
@@ -152,22 +169,22 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
* Note, -mfentry does not use frame pointers, and this test
* is not needed if CC_USING_FENTRY is set.
*/
- if (unlikely(current->ret_stack[index].fp != frame_pointer)) {
+ if (unlikely(ret_stack->fp != frame_pointer)) {
ftrace_graph_stop();
WARN(1, "Bad frame pointer: expected %lx, received %lx\n"
" from func %ps return to %lx\n",
current->ret_stack[index].fp,
frame_pointer,
- (void *)current->ret_stack[index].func,
- current->ret_stack[index].ret);
+ (void *)ret_stack->func,
+ ret_stack->ret);
*ret = (unsigned long)panic;
return;
}
#endif

- *ret = current->ret_stack[index].ret;
- trace->func = current->ret_stack[index].func;
- trace->calltime = current->ret_stack[index].calltime;
+ *ret = ret_stack->ret;
+ trace->func = ret_stack->func;
+ trace->calltime = ret_stack->calltime;
trace->overrun = atomic_read(&current->trace_overrun);
trace->depth = current->curr_ret_depth--;
/*
@@ -221,7 +238,7 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
* curr_ret_stack is after that.
*/
barrier();
- current->curr_ret_stack--;
+ RET_STACK_DEC(current->curr_ret_stack);

if (unlikely(!ret)) {
ftrace_graph_stop();
@@ -236,12 +253,13 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
struct ftrace_ret_stack *
ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
{
- idx = current->curr_ret_stack - idx;
+ int index = task->curr_ret_stack;

- if (idx >= 0 && idx <= task->curr_ret_stack)
- return &current->ret_stack[idx];
+ index -= FGRAPH_RET_INDEX * (idx + 1);
+ if (index < 0)
+ return NULL;

- return NULL;
+ return RET_STACK(task, index);
}

/**
@@ -263,18 +281,20 @@ ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
unsigned long ret, unsigned long *retp)
{
+ struct ftrace_ret_stack *ret_stack;
int index = task->curr_ret_stack;
int i;

if (ret != (unsigned long)return_to_handler)
return ret;

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

- for (i = 0; i <= index; i++)
- if (task->ret_stack[i].retp == retp)
- return task->ret_stack[i].ret;
+ for (i = index; i >= 0; RET_STACK_DEC(i)) {
+ ret_stack = RET_STACK(task, i);
+ if (ret_stack->retp == retp)
+ return ret_stack->ret;
+ }

return ret;
}
@@ -288,14 +308,15 @@ unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
return ret;

task_idx = task->curr_ret_stack;
+ RET_STACK_DEC(task_idx);

if (!task->ret_stack || task_idx < *idx)
return ret;

task_idx -= *idx;
- (*idx)++;
+ RET_STACK_INC(*idx);

- return task->ret_stack[task_idx].ret;
+ return RET_STACK(task, task_idx);
}
#endif /* HAVE_FUNCTION_GRAPH_RET_ADDR_PTR */

@@ -329,7 +350,7 @@ trace_func_graph_ent_t ftrace_graph_entry = ftrace_graph_entry_stub;
static trace_func_graph_ent_t __ftrace_graph_entry = ftrace_graph_entry_stub;

/* Try to assign a return stack array on FTRACE_RETSTACK_ALLOC_SIZE tasks. */
-static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
+static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
{
int i;
int ret = 0;
@@ -337,10 +358,7 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
struct task_struct *g, *t;

for (i = 0; i < FTRACE_RETSTACK_ALLOC_SIZE; i++) {
- ret_stack_list[i] =
- kmalloc_array(FTRACE_RETFUNC_DEPTH,
- sizeof(struct ftrace_ret_stack),
- GFP_KERNEL);
+ ret_stack_list[i] = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
if (!ret_stack_list[i]) {
start = 0;
end = i;
@@ -359,9 +377,9 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
if (t->ret_stack == NULL) {
atomic_set(&t->tracing_graph_pause, 0);
atomic_set(&t->trace_overrun, 0);
- t->curr_ret_stack = -1;
+ t->curr_ret_stack = 0;
t->curr_ret_depth = -1;
- /* Make sure the tasks see the -1 first: */
+ /* Make sure the tasks see the 0 first: */
smp_wmb();
t->ret_stack = ret_stack_list[start++];
}
@@ -379,6 +397,7 @@ static void
ftrace_graph_probe_sched_switch(void *ignore, bool preempt,
struct task_struct *prev, struct task_struct *next)
{
+ struct ftrace_ret_stack *ret_stack;
unsigned long long timestamp;
int index;

@@ -403,8 +422,11 @@ ftrace_graph_probe_sched_switch(void *ignore, bool preempt,
*/
timestamp -= next->ftrace_timestamp;

- for (index = next->curr_ret_stack; index >= 0; index--)
- next->ret_stack[index].calltime += timestamp;
+ for (index = next->curr_ret_stack - FGRAPH_RET_INDEX; index >= 0; ) {
+ ret_stack = RET_STACK(next, index);
+ ret_stack->calltime += timestamp;
+ index -= FGRAPH_RET_INDEX;
+ }
}

static int ftrace_graph_entry_test(struct ftrace_graph_ent *trace)
@@ -447,10 +469,10 @@ void update_function_graph_func(void)
ftrace_graph_entry = __ftrace_graph_entry;
}

-static DEFINE_PER_CPU(struct ftrace_ret_stack *, idle_ret_stack);
+static DEFINE_PER_CPU(unsigned long *, idle_ret_stack);

static void
-graph_init_task(struct task_struct *t, struct ftrace_ret_stack *ret_stack)
+graph_init_task(struct task_struct *t, unsigned long *ret_stack)
{
atomic_set(&t->tracing_graph_pause, 0);
atomic_set(&t->trace_overrun, 0);
@@ -466,7 +488,7 @@ graph_init_task(struct task_struct *t, struct ftrace_ret_stack *ret_stack)
*/
void ftrace_graph_init_idle_task(struct task_struct *t, int cpu)
{
- t->curr_ret_stack = -1;
+ t->curr_ret_stack = 0;
t->curr_ret_depth = -1;
/*
* The idle task has no parent, it either has its own
@@ -476,14 +498,11 @@ void ftrace_graph_init_idle_task(struct task_struct *t, int cpu)
WARN_ON(t->ret_stack != per_cpu(idle_ret_stack, cpu));

if (ftrace_graph_active) {
- struct ftrace_ret_stack *ret_stack;
+ unsigned long *ret_stack;

ret_stack = per_cpu(idle_ret_stack, cpu);
if (!ret_stack) {
- ret_stack =
- kmalloc_array(FTRACE_RETFUNC_DEPTH,
- sizeof(struct ftrace_ret_stack),
- GFP_KERNEL);
+ ret_stack = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
if (!ret_stack)
return;
per_cpu(idle_ret_stack, cpu) = ret_stack;
@@ -497,15 +516,13 @@ void ftrace_graph_init_task(struct task_struct *t)
{
/* Make sure we do not use the parent ret_stack */
t->ret_stack = NULL;
- t->curr_ret_stack = -1;
+ t->curr_ret_stack = 0;
t->curr_ret_depth = -1;

if (ftrace_graph_active) {
- struct ftrace_ret_stack *ret_stack;
+ unsigned long *ret_stack;

- ret_stack = kmalloc_array(FTRACE_RETFUNC_DEPTH,
- sizeof(struct ftrace_ret_stack),
- GFP_KERNEL);
+ ret_stack = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
if (!ret_stack)
return;
graph_init_task(t, ret_stack);
@@ -514,7 +531,7 @@ void ftrace_graph_init_task(struct task_struct *t)

void ftrace_graph_exit_task(struct task_struct *t)
{
- struct ftrace_ret_stack *ret_stack = t->ret_stack;
+ unsigned long *ret_stack = t->ret_stack;

t->ret_stack = NULL;
/* NULL must become visible to IRQs before we free it: */
@@ -526,12 +543,10 @@ void ftrace_graph_exit_task(struct task_struct *t)
/* Allocate a return stack for each task */
static int start_graph_tracing(void)
{
- struct ftrace_ret_stack **ret_stack_list;
+ unsigned long **ret_stack_list;
int ret, cpu;

- ret_stack_list = kmalloc_array(FTRACE_RETSTACK_ALLOC_SIZE,
- sizeof(struct ftrace_ret_stack *),
- GFP_KERNEL);
+ ret_stack_list = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);

if (!ret_stack_list)
return -ENOMEM;
--
2.19.1