path: root/kernel/trace/fgraph.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Infrastructure to took into function calls and returns.
 * Copyright (c) 2008-2009 Frederic Weisbecker <fweisbec@gmail.com>
 * Mostly borrowed from function tracer which
 * is Copyright (c) Steven Rostedt <srostedt@redhat.com>
 *
 * Highly modified by Steven Rostedt (VMware).
 */
#include <linux/bits.h>
#include <linux/jump_label.h>
#include <linux/suspend.h>
#include <linux/ftrace.h>
#include <linux/slab.h>

#include <trace/events/sched.h>

#include "ftrace_internal.h"
#include "trace.h"

/*
 * FGRAPH_FRAME_SIZE:	Size in bytes of the meta data on the shadow stack
 * FGRAPH_FRAME_OFFSET:	Size in long words of the meta data frame
 */
#define FGRAPH_FRAME_SIZE	sizeof(struct ftrace_ret_stack)
#define FGRAPH_FRAME_OFFSET	DIV_ROUND_UP(FGRAPH_FRAME_SIZE, sizeof(long))

/*
 * On entry to a function (via function_graph_enter()), a new fgraph frame
 * (ftrace_ret_stack) is pushed onto the stack as well as a word that
 * holds a bitmask and a type (called "bitmap"). The bitmap is defined as:
 *
 * bits:  0 -  9	offset in words from the previous ftrace_ret_stack
 *			Currently, this will always be set to FGRAPH_FRAME_OFFSET
 *			to get to the fgraph frame.
 *
 * bits: 10 - 11	Type of storage
 *			  0 - reserved
 *			  1 - bitmap of fgraph_array index
 *
 * For type with "bitmap of fgraph_array index" (FGRAPH_TYPE_BITMAP):
 *  bits: 12 - 27	The bitmap of fgraph_ops fgraph_array index
 *			That is, it's a bitmask of 0-15 (16 bits)
 *			where if a corresponding ops in the fgraph_array[]
 *			expects a callback from the return of the function
 *			it's corresponding bit will be set.
 *
 *
 * The top of the ret_stack (when not empty) will always have a reference
 * word that points to the last fgraph frame that was saved.
 *
 * That is, at the end of function_graph_enter, if the first and forth
 * fgraph_ops on the fgraph_array[] (index 0 and 3) needs their retfunc called
 * on the return of the function being traced, this is what will be on the
 * task's shadow ret_stack: (the stack grows upward)
 *
 *  ret_stack[SHADOW_STACK_MAX_OFFSET]
 * ...
 * |                                            | <- task->curr_ret_stack
 * +--------------------------------------------+
 * | (9 << 12) | (1 << 10) | FGRAPH_FRAME_OFFSET|
 * |         *or put another way*               |
 * | (BIT(3)|BIT(0)) << FGRAPH_INDEX_SHIFT | \  |
 * | FGRAPH_TYPE_BITMAP << FGRAPH_TYPE_SHIFT| \ |
 * | (offset:FGRAPH_FRAME_OFFSET)               | <- the offset is from here
 * +--------------------------------------------+
 * | struct ftrace_ret_stack                    |
 * |   (stores the saved ret pointer)           | <- the offset points here
 * +--------------------------------------------+
 * |                 (X) | (N)                  | ( N words away from
 * |                                            |   previous ret_stack)
 * ...
 * ret_stack[0]
 *
 * If a backtrace is required, and the real return pointer needs to be
 * fetched, then it looks at the task's curr_ret_stack offset, if it
 * is greater than zero (reserved, or right before popped), it would mask
 * the value by FGRAPH_FRAME_OFFSET_MASK to get the offset of the
 * ftrace_ret_stack structure stored on the shadow stack.
 */

/*
 * The following is for the top word on the stack:
 *
 *   FGRAPH_FRAME_OFFSET (0-9) holds the offset delta to the fgraph frame
 *   FGRAPH_TYPE (10-11) holds the type of word this is.
 *     (RESERVED or BITMAP)
 */
#define FGRAPH_FRAME_OFFSET_BITS	10
#define FGRAPH_FRAME_OFFSET_MASK	GENMASK(FGRAPH_FRAME_OFFSET_BITS - 1, 0)

#define FGRAPH_TYPE_BITS	2
#define FGRAPH_TYPE_MASK	GENMASK(FGRAPH_TYPE_BITS - 1, 0)
#define FGRAPH_TYPE_SHIFT	FGRAPH_FRAME_OFFSET_BITS

enum {
	FGRAPH_TYPE_RESERVED	= 0,
	FGRAPH_TYPE_BITMAP	= 1,
};

/*
 * For BITMAP type:
 *   FGRAPH_INDEX (12-27) bits holding the gops index wanting return callback called
 */
#define FGRAPH_INDEX_BITS	16
#define FGRAPH_INDEX_MASK	GENMASK(FGRAPH_INDEX_BITS - 1, 0)
#define FGRAPH_INDEX_SHIFT	(FGRAPH_TYPE_SHIFT + FGRAPH_TYPE_BITS)

#define FGRAPH_ARRAY_SIZE	FGRAPH_INDEX_BITS

/*
 * SHADOW_STACK_SIZE:	The size in bytes of the entire shadow stack
 * SHADOW_STACK_OFFSET:	The size in long words of the shadow stack
 * SHADOW_STACK_MAX_OFFSET: The max offset of the stack for a new frame to be added
 */
#define SHADOW_STACK_SIZE	(PAGE_SIZE)
#define SHADOW_STACK_OFFSET	(SHADOW_STACK_SIZE / sizeof(long))
/* Leave on a buffer at the end */
#define SHADOW_STACK_MAX_OFFSET (SHADOW_STACK_OFFSET - (FGRAPH_FRAME_OFFSET + 1))

/* RET_STACK():		Return the frame from a given @offset from task @t */
#define RET_STACK(t, offset) ((struct ftrace_ret_stack *)(&(t)->ret_stack[offset]))

DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph);
int ftrace_graph_active;

static int fgraph_array_cnt;

static struct fgraph_ops *fgraph_array[FGRAPH_ARRAY_SIZE];

/* Get the FRAME_OFFSET from the word from the @offset on ret_stack */
static inline int get_frame_offset(struct task_struct *t, int offset)
{
	return t->ret_stack[offset] & FGRAPH_FRAME_OFFSET_MASK;
}

/* Get FGRAPH_TYPE from the word from the @offset at ret_stack */
static inline int get_fgraph_type(struct task_struct *t, int offset)
{
	return (t->ret_stack[offset] >> FGRAPH_TYPE_SHIFT) & FGRAPH_TYPE_MASK;
}

/* For BITMAP type: get the bitmask from the @offset at ret_stack */
static inline unsigned long
get_bitmap_bits(struct task_struct *t, int offset)
{
	return (t->ret_stack[offset] >> FGRAPH_INDEX_SHIFT) & FGRAPH_INDEX_MASK;
}

/* For BITMAP type: set the bits in the bitmap bitmask at @offset on ret_stack */
static inline void
set_bitmap_bits(struct task_struct *t, int offset, unsigned long bitmap)
{
	t->ret_stack[offset] |= (bitmap << FGRAPH_INDEX_SHIFT);
}

/* Write the bitmap to the ret_stack at @offset (does index, offset and bitmask) */
static inline void
set_bitmap(struct task_struct *t, int offset, unsigned long bitmap)
{
	t->ret_stack[offset] = (bitmap << FGRAPH_INDEX_SHIFT) |
		(FGRAPH_TYPE_BITMAP << FGRAPH_TYPE_SHIFT) | FGRAPH_FRAME_OFFSET;
}

/* ftrace_graph_entry set to this to tell some archs to run function graph */
static int entry_run(struct ftrace_graph_ent *trace, struct fgraph_ops *ops)
{
	return 0;
}

/* ftrace_graph_return set to this to tell some archs to run function graph */
static void return_run(struct ftrace_graph_ret *trace, struct fgraph_ops *ops)
{
}

/*
 * @offset: The offset into @t->ret_stack to find the ret_stack entry
 * @frame_offset: Where to place the offset into @t->ret_stack of that entry
 *
 * Returns a pointer to the previous ret_stack below @offset or NULL
 *   when it reaches the bottom of the stack.
 *
 * Calling this with:
 *
 *   offset = task->curr_ret_stack;
 *   do {
 *	ret_stack = get_ret_stack(task, offset, &offset);
 *   } while (ret_stack);
 *
 * Will iterate through all the ret_stack entries from curr_ret_stack
 * down to the first one.
 */
static inline struct ftrace_ret_stack *
get_ret_stack(struct task_struct *t, int offset, int *frame_offset)
{
	int offs;

	BUILD_BUG_ON(FGRAPH_FRAME_SIZE % sizeof(long));

	if (unlikely(offset <= 0))
		return NULL;

	offs = get_frame_offset(t, --offset);
	if (WARN_ON_ONCE(offs <= 0 || offs > offset))
		return NULL;

	offset -= offs;

	*frame_offset = offset;
	return RET_STACK(t, offset);
}

/* Both enabled by default (can be cleared by function_graph tracer flags */
static bool fgraph_sleep_time = true;

#ifdef CONFIG_DYNAMIC_FTRACE
/*
 * archs can override this function if they must do something
 * to enable hook for graph tracer.
 */
int __weak ftrace_enable_ftrace_graph_caller(void)
{
	return 0;
}

/*
 * archs can override this function if they must do something
 * to disable hook for graph tracer.
 */
int __weak ftrace_disable_ftrace_graph_caller(void)
{
	return 0;
}
#endif

int ftrace_graph_entry_stub(struct ftrace_graph_ent *trace,
			    struct fgraph_ops *gops)
{
	return 0;
}

static void ftrace_graph_ret_stub(struct ftrace_graph_ret *trace,
				  struct fgraph_ops *gops)
{
}

static struct fgraph_ops fgraph_stub = {
	.entryfunc = ftrace_graph_entry_stub,
	.retfunc = ftrace_graph_ret_stub,
};

/**
 * ftrace_graph_stop - set to permanently disable function graph tracing
 *
 * In case of an error int function graph tracing, this is called
 * to try to keep function graph tracing from causing any more harm.
 * Usually this is pretty severe and this is called to try to at least
 * get a warning out to the user.
 */
void ftrace_graph_stop(void)
{
	static_branch_enable(&kill_ftrace_graph);
}

/* Add a function return address to the trace stack on thread info.*/
static int
ftrace_push_return_trace(unsigned long ret, unsigned long func,
			 unsigned long frame_pointer, unsigned long *retp,
			 int fgraph_idx)
{
	struct ftrace_ret_stack *ret_stack;
	unsigned long long calltime;
	unsigned long val;
	int offset;

	if (unlikely(ftrace_graph_is_dead()))
		return -EBUSY;

	if (!current->ret_stack)
		return -EBUSY;

	BUILD_BUG_ON(SHADOW_STACK_SIZE % sizeof(long));

	/* Set val to "reserved" with the delta to the new fgraph frame */
	val = (FGRAPH_TYPE_RESERVED << FGRAPH_TYPE_SHIFT) | FGRAPH_FRAME_OFFSET;

	/*
	 * We must make sure the ret_stack is tested before we read
	 * anything else.
	 */
	smp_rmb();

	/*
	 * Check if there's room on the shadow stack to fit a fraph frame
	 * and a bitmap word.
	 */
	if (current->curr_ret_stack + FGRAPH_FRAME_OFFSET + 1 >= SHADOW_STACK_MAX_OFFSET) {
		atomic_inc(&current->trace_overrun);
		return -EBUSY;
	}

	calltime = trace_clock_local();

	offset = READ_ONCE(current->curr_ret_stack);
	ret_stack = RET_STACK(current, offset);
	offset += FGRAPH_FRAME_OFFSET;

	/* ret offset = FGRAPH_FRAME_OFFSET ; type = reserved */
	current->ret_stack[offset] = val;
	ret_stack->ret = ret;
	/*
	 * The unwinders expect curr_ret_stack to point to either zero
	 * or an offset where to find the next ret_stack. Even though the
	 * ret stack might be bogus, we want to write the ret and the
	 * offset to find the ret_stack before we increment the stack point.
	 * If an interrupt comes in now before we increment the curr_ret_stack
	 * it may blow away what we wrote. But that's fine, because the
	 * offset will still be correct (even though the 'ret' won't be).
	 * What we worry about is the offset being correct after we increment
	 * the curr_ret_stack and before we update that offset, as if an
	 * interrupt comes in and does an unwind stack dump, it will need
	 * at least a correct offset!
	 */
	barrier();
	WRITE_ONCE(current->curr_ret_stack, offset + 1);
	/*
	 * This next barrier is to ensure that an interrupt coming in
	 * will not corrupt what we are about to write.
	 */
	barrier();

	/* Still keep it reserved even if an interrupt came in */
	current->ret_stack[offset] = val;

	ret_stack->ret = ret;
	ret_stack->func = func;
	ret_stack->calltime = calltime;
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
	ret_stack->fp = frame_pointer;
#endif
#ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
	ret_stack->retp = retp;
#endif
	return offset;
}

/*
 * Not all archs define MCOUNT_INSN_SIZE which is used to look for direct
 * functions. But those archs currently don't support direct functions
 * anyway, and ftrace_find_rec_direct() is just a stub for them.
 * Define MCOUNT_INSN_SIZE to keep those archs compiling.
 */
#ifndef MCOUNT_INSN_SIZE
/* Make sure this only works without direct calls */
# ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
#  error MCOUNT_INSN_SIZE not defined with direct calls enabled
# endif
# define MCOUNT_INSN_SIZE 0
#endif

/* If the caller does not use ftrace, call this function. */
int function_graph_enter(unsigned long ret, unsigned long func,
			 unsigned long frame_pointer, unsigned long *retp)
{
	struct ftrace_graph_ent trace;
	unsigned long bitmap = 0;
	int offset;
	int i;

	trace.func = func;
	trace.depth = ++current->curr_ret_depth;

	offset = ftrace_push_return_trace(ret, func, frame_pointer, retp, 0);
	if (offset < 0)
		goto out;

	for (i = 0; i < fgraph_array_cnt; i++) {
		struct fgraph_ops *gops = fgraph_array[i];

		if (gops == &fgraph_stub)
			continue;

		if (ftrace_ops_test(&gops->ops, func, NULL) &&
		    gops->entryfunc(&trace, gops))
			bitmap |= BIT(i);
	}

	if (!bitmap)
		goto out_ret;

	/*
	 * Since this function uses fgraph_idx = 0 as a tail-call checking
	 * flag, set that bit always.
	 */
	set_bitmap(current, offset, bitmap | BIT(0));

	return 0;
 out_ret:
	current->curr_ret_stack -= FGRAPH_FRAME_OFFSET + 1;
 out:
	current->curr_ret_depth--;
	return -EBUSY;
}

/* Retrieve a function return address to the trace stack on thread info.*/
static struct ftrace_ret_stack *
ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
			unsigned long frame_pointer, int *offset)
{
	struct ftrace_ret_stack *ret_stack;

	ret_stack = get_ret_stack(current, current->curr_ret_stack, offset);

	if (unlikely(!ret_stack)) {
		ftrace_graph_stop();
		WARN(1, "Bad function graph ret_stack pointer: %d",
		     current->curr_ret_stack);
		/* Might as well panic, otherwise we have no where to go */
		*ret = (unsigned long)panic;
		return NULL;
	}

#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
	/*
	 * The arch may choose to record the frame pointer used
	 * and check it here to make sure that it is what we expect it
	 * to be. If gcc does not set the place holder of the return
	 * address in the frame pointer, and does a copy instead, then
	 * the function graph trace will fail. This test detects this
	 * case.
	 *
	 * Currently, x86_32 with optimize for size (-Os) makes the latest
	 * gcc do the above.
	 *
	 * Note, -mfentry does not use frame pointers, and this test
	 *  is not needed if CC_USING_FENTRY is set.
	 */
	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",
		     ret_stack->fp,
		     frame_pointer,
		     (void *)ret_stack->func,
		     ret_stack->ret);
		*ret = (unsigned long)panic;
		return NULL;
	}
#endif

	*offset += FGRAPH_FRAME_OFFSET;
	*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;
	/*
	 * We still want to trace interrupts coming in if
	 * max_depth is set to 1. Make sure the decrement is
	 * seen before ftrace_graph_return.
	 */
	barrier();

	return ret_stack;
}

/*
 * Hibernation protection.
 * The state of the current task is too much unstable during
 * suspend/restore to disk. We want to protect against that.
 */
static int
ftrace_suspend_notifier_call(struct notifier_block *bl, unsigned long state,
							void *unused)
{
	switch (state) {
	case PM_HIBERNATION_PREPARE:
		pause_graph_tracing();
		break;

	case PM_POST_HIBERNATION:
		unpause_graph_tracing();
		break;
	}
	return NOTIFY_DONE;
}

static struct notifier_block ftrace_suspend_notifier = {
	.notifier_call = ftrace_suspend_notifier_call,
};

/* fgraph_ret_regs is not defined without CONFIG_FUNCTION_GRAPH_RETVAL */
struct fgraph_ret_regs;

/*
 * Send the trace to the ring-buffer.
 * @return the original return address.
 */
static unsigned long __ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs,
						unsigned long frame_pointer)
{
	struct ftrace_ret_stack *ret_stack;
	struct ftrace_graph_ret trace;
	unsigned long bitmap;
	unsigned long ret;
	int offset;
	int i;

	ret_stack = ftrace_pop_return_trace(&trace, &ret, frame_pointer, &offset);

	if (unlikely(!ret_stack)) {
		ftrace_graph_stop();
		WARN_ON(1);
		/* Might as well panic. What else to do? */
		return (unsigned long)panic;
	}

	trace.rettime = trace_clock_local();
#ifdef CONFIG_FUNCTION_GRAPH_RETVAL
	trace.retval = fgraph_ret_regs_return_value(ret_regs);
#endif

	bitmap = get_bitmap_bits(current, offset);
	for (i = 0; i < FGRAPH_ARRAY_SIZE; i++) {
		struct fgraph_ops *gops = fgraph_array[i];

		if (!(bitmap & BIT(i)))
			continue;
		if (gops == &fgraph_stub)
			continue;

		gops->retfunc(&trace, gops);
	}

	/*
	 * The ftrace_graph_return() may still access the current
	 * ret_stack structure, we need to make sure the update of
	 * curr_ret_stack is after that.
	 */
	barrier();
	current->curr_ret_stack -= FGRAPH_FRAME_OFFSET + 1;
	current->curr_ret_depth--;
	return ret;
}

/*
 * After all architecures have selected HAVE_FUNCTION_GRAPH_RETVAL, we can
 * leave only ftrace_return_to_handler(ret_regs).
 */
#ifdef CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
unsigned long ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs)
{
	return __ftrace_return_to_handler(ret_regs,
				fgraph_ret_regs_frame_pointer(ret_regs));
}
#else
unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
{
	return __ftrace_return_to_handler(NULL, frame_pointer);
}
#endif

/**
 * ftrace_graph_get_ret_stack - return the entry of the shadow stack
 * @task: The task to read the shadow stack from.
 * @idx: Index down the shadow stack
 *
 * Return the ret_struct on the shadow stack of the @task at the
 * call graph at @idx starting with zero. If @idx is zero, it
 * will return the last saved ret_stack entry. If it is greater than
 * zero, it will return the corresponding ret_stack for the depth
 * of saved return addresses.
 */
struct ftrace_ret_stack *
ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
{
	struct ftrace_ret_stack *ret_stack = NULL;
	int offset = task->curr_ret_stack;

	if (offset < 0)
		return NULL;

	do {
		ret_stack = get_ret_stack(task, offset, &offset);
	} while (ret_stack && --idx >= 0);

	return ret_stack;
}

/**
 * ftrace_graph_ret_addr - convert a potentially modified stack return address
 *			   to its original value
 *
 * This function can be called by stack unwinding code to convert a found stack
 * return address ('ret') to its original value, in case the function graph
 * tracer has modified it to be 'return_to_handler'.  If the address hasn't
 * been modified, the unchanged value of 'ret' is returned.
 *
 * 'idx' is a state variable which should be initialized by the caller to zero
 * before the first call.
 *
 * 'retp' is a pointer to the return address on the stack.  It's ignored if
 * the arch doesn't have HAVE_FUNCTION_GRAPH_RET_ADDR_PTR defined.
 */
#ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
				    unsigned long ret, unsigned long *retp)
{
	struct ftrace_ret_stack *ret_stack;
	unsigned long return_handler = (unsigned long)dereference_kernel_function_descriptor(return_to_handler);
	int i = task->curr_ret_stack;

	if (ret != return_handler)
		return ret;

	while (i > 0) {
		ret_stack = get_ret_stack(current, i, &i);
		if (!ret_stack)
			break;
		/*
		 * For the tail-call, there would be 2 or more ftrace_ret_stacks on
		 * the ret_stack, which records "return_to_handler" as the return
		 * address except for the last one.
		 * But on the real stack, there should be 1 entry because tail-call
		 * reuses the return address on the stack and jump to the next function.
		 * Thus we will continue to find real return address.
		 */
		if (ret_stack->retp == retp &&
		    ret_stack->ret != return_handler)
			return ret_stack->ret;
	}

	return ret;
}
#else /* !HAVE_FUNCTION_GRAPH_RET_ADDR_PTR */
unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
				    unsigned long ret, unsigned long *retp)
{
	struct ftrace_ret_stack *ret_stack;
	unsigned long return_handler = (unsigned long)dereference_kernel_function_descriptor(return_to_handler);
	int offset = task->curr_ret_stack;
	int i;

	if (ret != return_handler)
		return ret;

	if (!idx)
		return ret;

	i = *idx;
	do {
		ret_stack = get_ret_stack(task, offset, &offset);
		if (ret_stack && ret_stack->ret == return_handler)
			continue;
		i--;
	} while (i >= 0 && ret_stack);

	if (ret_stack)
		return ret_stack->ret;

	return ret;
}
#endif /* HAVE_FUNCTION_GRAPH_RET_ADDR_PTR */

static struct ftrace_ops graph_ops = {
	.func			= ftrace_graph_func,
	.flags			= FTRACE_OPS_GRAPH_STUB,
#ifdef FTRACE_GRAPH_TRAMP_ADDR
	.trampoline		= FTRACE_GRAPH_TRAMP_ADDR,
	/* trampoline_size is only needed for dynamically allocated tramps */
#endif
};

void fgraph_init_ops(struct ftrace_ops *dst_ops,
		     struct ftrace_ops *src_ops)
{
	dst_ops->flags = FTRACE_OPS_FL_PID | FTRACE_OPS_GRAPH_STUB;

#ifdef CONFIG_DYNAMIC_FTRACE
	if (src_ops) {
		dst_ops->func_hash = &src_ops->local_hash;
		mutex_init(&dst_ops->local_hash.regex_lock);
		INIT_LIST_HEAD(&dst_ops->subop_list);
		dst_ops->flags |= FTRACE_OPS_FL_INITIALIZED;
	}
#endif
}

void ftrace_graph_sleep_time_control(bool enable)
{
	fgraph_sleep_time = enable;
}

/*
 * Simply points to ftrace_stub, but with the proper protocol.
 * Defined by the linker script in linux/vmlinux.lds.h
 */
void ftrace_stub_graph(struct ftrace_graph_ret *trace, struct fgraph_ops *gops);

/* The callbacks that hook a function */
trace_func_graph_ret_t ftrace_graph_return = ftrace_stub_graph;
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(unsigned long **ret_stack_list)
{
	int i;
	int ret = 0;
	int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE;
	struct task_struct *g, *t;

	for (i = 0; i < FTRACE_RETSTACK_ALLOC_SIZE; i++) {
		ret_stack_list[i] = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
		if (!ret_stack_list[i]) {
			start = 0;
			end = i;
			ret = -ENOMEM;
			goto free;
		}
	}

	rcu_read_lock();
	for_each_process_thread(g, t) {
		if (start == end) {
			ret = -EAGAIN;
			goto unlock;
		}

		if (t->ret_stack == NULL) {
			atomic_set(&t->trace_overrun, 0);
			t->curr_ret_stack = 0;
			t->curr_ret_depth = -1;
			/* Make sure the tasks see the 0 first: */
			smp_wmb();
			t->ret_stack = ret_stack_list[start++];
		}
	}

unlock:
	rcu_read_unlock();
free:
	for (i = start; i < end; i++)
		kfree(ret_stack_list[i]);
	return ret;
}

static void
ftrace_graph_probe_sched_switch(void *ignore, bool preempt,
				struct task_struct *prev,
				struct task_struct *next,
				unsigned int prev_state)
{
	struct ftrace_ret_stack *ret_stack;
	unsigned long long timestamp;
	int offset;

	/*
	 * Does the user want to count the time a function was asleep.
	 * If so, do not update the time stamps.
	 */
	if (fgraph_sleep_time)
		return;

	timestamp = trace_clock_local();

	prev->ftrace_timestamp = timestamp;

	/* only process tasks that we timestamped */
	if (!next->ftrace_timestamp)
		return;

	/*
	 * Update all the counters in next to make up for the
	 * time next was sleeping.
	 */
	timestamp -= next->ftrace_timestamp;

	for (offset = next->curr_ret_stack; offset > 0; ) {
		ret_stack = get_ret_stack(next, offset, &offset);
		if (ret_stack)
			ret_stack->calltime += timestamp;
	}
}

static DEFINE_PER_CPU(unsigned long *, idle_ret_stack);

static void
graph_init_task(struct task_struct *t, unsigned long *ret_stack)
{
	atomic_set(&t->trace_overrun, 0);
	t->ftrace_timestamp = 0;
	t->curr_ret_stack = 0;
	t->curr_ret_depth = -1;
	/* make curr_ret_stack visible before we add the ret_stack */
	smp_wmb();
	t->ret_stack = ret_stack;
}

/*
 * Allocate a return stack for the idle task. May be the first
 * time through, or it may be done by CPU hotplug online.
 */
void ftrace_graph_init_idle_task(struct task_struct *t, int cpu)
{
	t->curr_ret_stack = 0;
	t->curr_ret_depth = -1;
	/*
	 * The idle task has no parent, it either has its own
	 * stack or no stack at all.
	 */
	if (t->ret_stack)
		WARN_ON(t->ret_stack != per_cpu(idle_ret_stack, cpu));

	if (ftrace_graph_active) {
		unsigned long *ret_stack;

		ret_stack = per_cpu(idle_ret_stack, cpu);
		if (!ret_stack) {
			ret_stack = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
			if (!ret_stack)
				return;
			per_cpu(idle_ret_stack, cpu) = ret_stack;
		}
		graph_init_task(t, ret_stack);
	}
}

/* Allocate a return stack for newly created task */
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 = 0;
	t->curr_ret_depth = -1;

	if (ftrace_graph_active) {
		unsigned long *ret_stack;

		ret_stack = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
		if (!ret_stack)
			return;
		graph_init_task(t, ret_stack);
	}
}

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

	t->ret_stack = NULL;
	/* NULL must become visible to IRQs before we free it: */
	barrier();

	kfree(ret_stack);
}

/* Allocate a return stack for each task */
static int start_graph_tracing(void)
{
	unsigned long **ret_stack_list;
	int ret, cpu;

	ret_stack_list = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);

	if (!ret_stack_list)
		return -ENOMEM;

	/* The cpu_boot init_task->ret_stack will never be freed */
	for_each_online_cpu(cpu) {
		if (!idle_task(cpu)->ret_stack)
			ftrace_graph_init_idle_task(idle_task(cpu), cpu);
	}

	do {
		ret = alloc_retstack_tasklist(ret_stack_list);
	} while (ret == -EAGAIN);

	if (!ret) {
		ret = register_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
		if (ret)
			pr_info("ftrace_graph: Couldn't activate tracepoint"
				" probe to kernel_sched_switch\n");
	}

	kfree(ret_stack_list);
	return ret;
}

int register_ftrace_graph(struct fgraph_ops *gops)
{
	int command = 0;
	int ret = 0;
	int i;

	mutex_lock(&ftrace_lock);

	if (!fgraph_array[0]) {
		/* The array must always have real data on it */
		for (i = 0; i < FGRAPH_ARRAY_SIZE; i++)
			fgraph_array[i] = &fgraph_stub;
	}

	/* Look for an available spot */
	for (i = 0; i < FGRAPH_ARRAY_SIZE; i++) {
		if (fgraph_array[i] == &fgraph_stub)
			break;
	}
	if (i >= FGRAPH_ARRAY_SIZE) {
		ret = -ENOSPC;
		goto out;
	}

	fgraph_array[i] = gops;
	if (i + 1 > fgraph_array_cnt)
		fgraph_array_cnt = i + 1;
	gops->idx = i;

	ftrace_graph_active++;

	if (ftrace_graph_active == 1) {
		register_pm_notifier(&ftrace_suspend_notifier);
		ret = start_graph_tracing();
		if (ret)
			goto error;
		/*
		 * Some archs just test to see if these are not
		 * the default function
		 */
		ftrace_graph_return = return_run;
		ftrace_graph_entry = entry_run;
		command = FTRACE_START_FUNC_RET;
	}

	ret = ftrace_startup_subops(&graph_ops, &gops->ops, command);
error:
	if (ret) {
		fgraph_array[i] = &fgraph_stub;
		ftrace_graph_active--;
	}
out:
	mutex_unlock(&ftrace_lock);
	return ret;
}

void unregister_ftrace_graph(struct fgraph_ops *gops)
{
	int command = 0;
	int i;

	mutex_lock(&ftrace_lock);

	if (unlikely(!ftrace_graph_active))
		goto out;

	if (unlikely(gops->idx < 0 || gops->idx >= fgraph_array_cnt))
		goto out;

	WARN_ON_ONCE(fgraph_array[gops->idx] != gops);

	fgraph_array[gops->idx] = &fgraph_stub;
	if (gops->idx + 1 == fgraph_array_cnt) {
		i = gops->idx;
		while (i >= 0 && fgraph_array[i] == &fgraph_stub)
			i--;
		fgraph_array_cnt = i + 1;
	}

	ftrace_graph_active--;

	if (!ftrace_graph_active)
		command = FTRACE_STOP_FUNC_RET;

	ftrace_shutdown_subops(&graph_ops, &gops->ops, command);

	if (!ftrace_graph_active) {
		ftrace_graph_return = ftrace_stub_graph;
		ftrace_graph_entry = ftrace_graph_entry_stub;
		unregister_pm_notifier(&ftrace_suspend_notifier);
		unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
	}
 out:
	mutex_unlock(&ftrace_lock);
}