drm/modes: Fix drm_mode_vrefres() docs

[drm/drm-misc.git] / 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/static_call.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
 *
 * bits: 10 - 11        Type of storage
 *                        0 - reserved
 *                        1 - bitmap of fgraph_array index
 *                        2 - reserved data
 *
 * 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.
 *
 * For reserved data:
 *  bits: 12 - 17       The size in words that is stored
 *  bits: 18 - 23       The index of fgraph_array, which shows who is stored
 *
 * 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, and the forth fgraph_ops
 * stored two words of data, this is what will be on the task's shadow
 * ret_stack: (the stack grows upward)
 *
 *  ret_stack[SHADOW_STACK_OFFSET]
 * | SHADOW_STACK_TASK_VARS(ret_stack)[15]      |
 * ...
 * | SHADOW_STACK_TASK_VARS(ret_stack)[0]       |
 *  ret_stack[SHADOW_STACK_MAX_OFFSET]
 * ...
 * |                                            | <- task->curr_ret_stack
 * +--------------------------------------------+
 * | (3 << 12) | (3 << 10) | FGRAPH_FRAME_OFFSET|
 * |         *or put another way*               |
 * | (3 << FGRAPH_DATA_INDEX_SHIFT)| \          | This is for fgraph_ops[3].
 * | ((2 - 1) << FGRAPH_DATA_SHIFT)| \          | The data size is 2 words.
 * | (FGRAPH_TYPE_DATA << FGRAPH_TYPE_SHIFT)| \ |
 * | (offset2:FGRAPH_FRAME_OFFSET+3)            | <- the offset2 is from here
 * +--------------------------------------------+ ( It is 4 words from the ret_stack)
 * |            STORED DATA WORD 2              |
 * |            STORED DATA WORD 1              |
 * +--------------------------------------------+
 * | (9 << 12) | (1 << 10) | FGRAPH_FRAME_OFFSET|
 * |         *or put another way*               |
 * | (BIT(3)|BIT(0)) << FGRAPH_INDEX_SHIFT | \  |
 * | FGRAPH_TYPE_BITMAP << FGRAPH_TYPE_SHIFT| \ |
 * | (offset1:FGRAPH_FRAME_OFFSET)              | <- the offset1 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,
        FGRAPH_TYPE_DATA        = 2,
};

/*
 * 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)

/*
 * For DATA type:
 *  FGRAPH_DATA (12-17) bits hold the size of data (in words)
 *  FGRAPH_INDEX (18-23) bits hold the index for which gops->idx the data is for
 *
 * Note:
 *  data_size == 0 means 1 word, and 31 (=2^5 - 1) means 32 words.
 */
#define FGRAPH_DATA_BITS        5
#define FGRAPH_DATA_MASK        GENMASK(FGRAPH_DATA_BITS - 1, 0)
#define FGRAPH_DATA_SHIFT       (FGRAPH_TYPE_SHIFT + FGRAPH_TYPE_BITS)
#define FGRAPH_MAX_DATA_SIZE (sizeof(long) * (1 << FGRAPH_DATA_BITS))

#define FGRAPH_DATA_INDEX_BITS  4
#define FGRAPH_DATA_INDEX_MASK  GENMASK(FGRAPH_DATA_INDEX_BITS - 1, 0)
#define FGRAPH_DATA_INDEX_SHIFT (FGRAPH_DATA_SHIFT + FGRAPH_DATA_BITS)

#define FGRAPH_MAX_INDEX        \
        ((FGRAPH_INDEX_SIZE << FGRAPH_DATA_BITS) + FGRAPH_RET_INDEX)

#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       (4096)
#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 + FGRAPH_ARRAY_SIZE))

/* 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]))

/*
 * Each fgraph_ops has a reservered unsigned long at the end (top) of the
 * ret_stack to store task specific state.
 */
#define SHADOW_STACK_TASK_VARS(ret_stack) \
        ((unsigned long *)(&(ret_stack)[SHADOW_STACK_OFFSET - FGRAPH_ARRAY_SIZE]))

DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph);
int ftrace_graph_active;

static struct kmem_cache *fgraph_stack_cachep;

static struct fgraph_ops *fgraph_array[FGRAPH_ARRAY_SIZE];
static unsigned long fgraph_array_bitmask;

/* LRU index table for fgraph_array */
static int fgraph_lru_table[FGRAPH_ARRAY_SIZE];
static int fgraph_lru_next;
static int fgraph_lru_last;

/* Initialize fgraph_lru_table with unused index */
static void fgraph_lru_init(void)
{
        int i;

        for (i = 0; i < FGRAPH_ARRAY_SIZE; i++)
                fgraph_lru_table[i] = i;
}

/* Release the used index to the LRU table */
static int fgraph_lru_release_index(int idx)
{
        if (idx < 0 || idx >= FGRAPH_ARRAY_SIZE ||
            WARN_ON_ONCE(fgraph_lru_table[fgraph_lru_last] != -1))
                return -1;

        fgraph_lru_table[fgraph_lru_last] = idx;
        fgraph_lru_last = (fgraph_lru_last + 1) % FGRAPH_ARRAY_SIZE;

        clear_bit(idx, &fgraph_array_bitmask);
        return 0;
}

/* Allocate a new index from LRU table */
static int fgraph_lru_alloc_index(void)
{
        int idx = fgraph_lru_table[fgraph_lru_next];

        /* No id is available */
        if (idx == -1)
                return -1;

        fgraph_lru_table[fgraph_lru_next] = -1;
        fgraph_lru_next = (fgraph_lru_next + 1) % FGRAPH_ARRAY_SIZE;

        set_bit(idx, &fgraph_array_bitmask);
        return idx;
}

/* Get the offset to the fgraph frame from a ret_stack value */
static inline int __get_offset(unsigned long val)
{
        return val & FGRAPH_FRAME_OFFSET_MASK;
}

/* Get the type of word from a ret_stack value */
static inline int __get_type(unsigned long val)
{
        return (val >> FGRAPH_TYPE_SHIFT) & FGRAPH_TYPE_MASK;
}

/* Get the data_index for a DATA type ret_stack word */
static inline int __get_data_index(unsigned long val)
{
        return (val >> FGRAPH_DATA_INDEX_SHIFT) & FGRAPH_DATA_INDEX_MASK;
}

/* Get the data_size for a DATA type ret_stack word */
static inline int __get_data_size(unsigned long val)
{
        return ((val >> FGRAPH_DATA_SHIFT) & FGRAPH_DATA_MASK) + 1;
}

/* Get the word from the ret_stack at @offset */
static inline unsigned long get_fgraph_entry(struct task_struct *t, int offset)
{
        return t->ret_stack[offset];
}

/* 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 __get_offset(t->ret_stack[offset]);
}

/* 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;
}

/* 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;
}

/* For DATA type: get the data saved under the ret_stack word at @offset */
static inline void *get_data_type_data(struct task_struct *t, int offset)
{
        unsigned long val = t->ret_stack[offset];

        if (__get_type(val) != FGRAPH_TYPE_DATA)
                return NULL;
        offset -= __get_data_size(val);
        return (void *)&t->ret_stack[offset];
}

/* Create the ret_stack word for a DATA type */
static inline unsigned long make_data_type_val(int idx, int size, int offset)
{
        return (idx << FGRAPH_DATA_INDEX_SHIFT) |
                ((size - 1) << FGRAPH_DATA_SHIFT) |
                (FGRAPH_TYPE_DATA << FGRAPH_TYPE_SHIFT) | 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)
{
}

static void ret_stack_set_task_var(struct task_struct *t, int idx, long val)
{
        unsigned long *gvals = SHADOW_STACK_TASK_VARS(t->ret_stack);

        gvals[idx] = val;
}

static unsigned long *
ret_stack_get_task_var(struct task_struct *t, int idx)
{
        unsigned long *gvals = SHADOW_STACK_TASK_VARS(t->ret_stack);

        return &gvals[idx];
}

static void ret_stack_init_task_vars(unsigned long *ret_stack)
{
        unsigned long *gvals = SHADOW_STACK_TASK_VARS(ret_stack);

        memset(gvals, 0, sizeof(*gvals) * FGRAPH_ARRAY_SIZE);
}

/**
 * fgraph_reserve_data - Reserve storage on the task's ret_stack
 * @idx:        The index of fgraph_array
 * @size_bytes: The size in bytes to reserve
 *
 * Reserves space of up to FGRAPH_MAX_DATA_SIZE bytes on the
 * task's ret_stack shadow stack, for a given fgraph_ops during
 * the entryfunc() call. If entryfunc() returns zero, the storage
 * is discarded. An entryfunc() can only call this once per iteration.
 * The fgraph_ops retfunc() can retrieve this stored data with
 * fgraph_retrieve_data().
 *
 * Returns: On success, a pointer to the data on the stack.
 *   Otherwise, NULL if there's not enough space left on the
 *   ret_stack for the data, or if fgraph_reserve_data() was called
 *   more than once for a single entryfunc() call.
 */
void *fgraph_reserve_data(int idx, int size_bytes)
{
        unsigned long val;
        void *data;
        int curr_ret_stack = current->curr_ret_stack;
        int data_size;

        if (size_bytes > FGRAPH_MAX_DATA_SIZE)
                return NULL;

        /* Convert the data size to number of longs. */
        data_size = (size_bytes + sizeof(long) - 1) >> (sizeof(long) == 4 ? 2 : 3);

        val = get_fgraph_entry(current, curr_ret_stack - 1);
        data = &current->ret_stack[curr_ret_stack];

        curr_ret_stack += data_size + 1;
        if (unlikely(curr_ret_stack >= SHADOW_STACK_MAX_OFFSET))
                return NULL;

        val = make_data_type_val(idx, data_size, __get_offset(val) + data_size + 1);

        /* Set the last word to be reserved */
        current->ret_stack[curr_ret_stack - 1] = val;

        /* Make sure interrupts see this */
        barrier();
        current->curr_ret_stack = curr_ret_stack;
        /* Again sync with interrupts, and reset reserve */
        current->ret_stack[curr_ret_stack - 1] = val;

        return data;
}

/**
 * fgraph_retrieve_data - Retrieve stored data from fgraph_reserve_data()
 * @idx:        the index of fgraph_array (fgraph_ops::idx)
 * @size_bytes: pointer to retrieved data size.
 *
 * This is to be called by a fgraph_ops retfunc(), to retrieve data that
 * was stored by the fgraph_ops entryfunc() on the function entry.
 * That is, this will retrieve the data that was reserved on the
 * entry of the function that corresponds to the exit of the function
 * that the fgraph_ops retfunc() is called on.
 *
 * Returns: The stored data from fgraph_reserve_data() called by the
 *    matching entryfunc() for the retfunc() this is called from.
 *   Or NULL if there was nothing stored.
 */
void *fgraph_retrieve_data(int idx, int *size_bytes)
{
        return fgraph_retrieve_parent_data(idx, size_bytes, 0);
}

/**
 * fgraph_get_task_var - retrieve a task specific state variable
 * @gops: The ftrace_ops that owns the task specific variable
 *
 * Every registered fgraph_ops has a task state variable
 * reserved on the task's ret_stack. This function returns the
 * address to that variable.
 *
 * Returns the address to the fgraph_ops @gops tasks specific
 * unsigned long variable.
 */
unsigned long *fgraph_get_task_var(struct fgraph_ops *gops)
{
        return ret_stack_get_task_var(current, gops->idx);
}

/*
 * @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);
}

/**
 * fgraph_retrieve_parent_data - get data from a parent function
 * @idx: The index into the fgraph_array (fgraph_ops::idx)
 * @size_bytes: A pointer to retrieved data size
 * @depth: The depth to find the parent (0 is the current function)
 *
 * This is similar to fgraph_retrieve_data() but can be used to retrieve
 * data from a parent caller function.
 *
 * Return: a pointer to the specified parent data or NULL if not found
 */
void *fgraph_retrieve_parent_data(int idx, int *size_bytes, int depth)
{
        struct ftrace_ret_stack *ret_stack = NULL;
        int offset = current->curr_ret_stack;
        unsigned long val;

        if (offset <= 0)
                return NULL;

        for (;;) {
                int next_offset;

                ret_stack = get_ret_stack(current, offset, &next_offset);
                if (!ret_stack || --depth < 0)
                        break;
                offset = next_offset;
        }

        if (!ret_stack)
                return NULL;

        offset--;

        val = get_fgraph_entry(current, offset);
        while (__get_type(val) == FGRAPH_TYPE_DATA) {
                if (__get_data_index(val) == idx)
                        goto found;
                offset -= __get_data_size(val) + 1;
                val = get_fgraph_entry(current, offset);
        }
        return NULL;
found:
        if (size_bytes)
                *size_bytes = __get_data_size(val) * sizeof(long);
        return get_data_type_data(current, offset);
}

/* Both enabled by default (can be cleared by function_graph tracer flags */
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,
};

static struct fgraph_ops *fgraph_direct_gops = &fgraph_stub;
DEFINE_STATIC_CALL(fgraph_func, ftrace_graph_entry_stub);
DEFINE_STATIC_CALL(fgraph_retfunc, ftrace_graph_ret_stub);
static DEFINE_STATIC_KEY_TRUE(fgraph_do_direct);

/**
 * 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 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;
        }

        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;
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
        ret_stack->fp = frame_pointer;
#endif
        ret_stack->retp = retp;
        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;

#ifdef CONFIG_HAVE_STATIC_CALL
        if (static_branch_likely(&fgraph_do_direct)) {
                int save_curr_ret_stack = current->curr_ret_stack;

                if (static_call(fgraph_func)(&trace, fgraph_direct_gops))
                        bitmap |= BIT(fgraph_direct_gops->idx);
                else
                        /* Clear out any saved storage */
                        current->curr_ret_stack = save_curr_ret_stack;
        } else
#endif
        {
                for_each_set_bit(i, &fgraph_array_bitmask,
                                         sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
                        struct fgraph_ops *gops = READ_ONCE(fgraph_array[i]);
                        int save_curr_ret_stack;

                        if (gops == &fgraph_stub)
                                continue;

                        save_curr_ret_stack = current->curr_ret_stack;
                        if (ftrace_ops_test(&gops->ops, func, NULL) &&
                            gops->entryfunc(&trace, gops))
                                bitmap |= BIT(i);
                        else
                                /* Clear out any saved storage */
                                current->curr_ret_stack = save_curr_ret_stack;
                }
        }

        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->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);

#ifdef CONFIG_HAVE_STATIC_CALL
        if (static_branch_likely(&fgraph_do_direct)) {
                if (test_bit(fgraph_direct_gops->idx, &bitmap))
                        static_call(fgraph_retfunc)(&trace, fgraph_direct_gops);
        } else
#endif
        {
                for_each_set_bit(i, &bitmap, sizeof(bitmap) * BITS_PER_BYTE) {
                        struct fgraph_ops *gops = fgraph_array[i];

                        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 = offset - FGRAPH_FRAME_OFFSET;

        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_top_ret_addr - return the top return address in the shadow stack
 * @task: The task to read the shadow stack from.
 *
 * Return the first return address on the shadow stack of the @task, which is
 * not the fgraph's return_to_handler.
 */
unsigned long ftrace_graph_top_ret_addr(struct task_struct *task)
{
        unsigned long return_handler = (unsigned long)dereference_kernel_function_descriptor(return_to_handler);
        struct ftrace_ret_stack *ret_stack = NULL;
        int offset = task->curr_ret_stack;

        if (offset < 0)
                return 0;

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

        return ret_stack ? ret_stack->ret : 0;
}

/**
 * ftrace_graph_ret_addr - return the original value of the return address
 * @task: The task the unwinder is being executed on
 * @idx: An initialized pointer to the next stack index to use
 * @ret: The current return address (likely pointing to return_handler)
 * @retp: The address on the stack of the current return location
 *
 * 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 holds the last index used to know where to start from. It should be
 * initialized to zero for the first iteration as that will mean to start
 * at the top of the shadow stack. If the location is found, this pointer
 * will be assigned that location so that if called again, it will continue
 * where it left off.
 *
 * @retp is a pointer to the return address on the stack.
 */
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;

        if (ret != return_handler)
                return ret;

        if (!idx)
                return ret;

        i = *idx ? : task->curr_ret_stack;
        while (i > 0) {
                ret_stack = get_ret_stack(task, 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) {
                        *idx = i;
                        return ret_stack->ret;
                }
        }

        return ret;
}

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;

        if (WARN_ON_ONCE(!fgraph_stack_cachep))
                return -ENOMEM;

        for (i = 0; i < FTRACE_RETSTACK_ALLOC_SIZE; i++) {
                ret_stack_list[i] = kmem_cache_alloc(fgraph_stack_cachep, 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);
                        ret_stack_init_task_vars(ret_stack_list[start]);
                        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++)
                kmem_cache_free(fgraph_stack_cachep, 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)
{
        unsigned long long timestamp;

        /*
         * 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;

        next->ftrace_sleeptime += timestamp - next->ftrace_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);
        ret_stack_init_task_vars(ret_stack);
        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;

                if (WARN_ON_ONCE(!fgraph_stack_cachep))
                        return;

                ret_stack = per_cpu(idle_ret_stack, cpu);
                if (!ret_stack) {
                        ret_stack = kmem_cache_alloc(fgraph_stack_cachep, 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;

                if (WARN_ON_ONCE(!fgraph_stack_cachep))
                        return;

                ret_stack = kmem_cache_alloc(fgraph_stack_cachep, 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();

        if (ret_stack) {
                if (WARN_ON_ONCE(!fgraph_stack_cachep))
                        return;
                kmem_cache_free(fgraph_stack_cachep, ret_stack);
        }
}

#ifdef CONFIG_DYNAMIC_FTRACE
static int fgraph_pid_func(struct ftrace_graph_ent *trace,
                           struct fgraph_ops *gops)
{
        struct trace_array *tr = gops->ops.private;
        int pid;

        if (tr) {
                pid = this_cpu_read(tr->array_buffer.data->ftrace_ignore_pid);
                if (pid == FTRACE_PID_IGNORE)
                        return 0;
                if (pid != FTRACE_PID_TRACE &&
                    pid != current->pid)
                        return 0;
        }

        return gops->saved_func(trace, gops);
}

void fgraph_update_pid_func(void)
{
        struct fgraph_ops *gops;
        struct ftrace_ops *op;

        if (!(graph_ops.flags & FTRACE_OPS_FL_INITIALIZED))
                return;

        list_for_each_entry(op, &graph_ops.subop_list, list) {
                if (op->flags & FTRACE_OPS_FL_PID) {
                        gops = container_of(op, struct fgraph_ops, ops);
                        gops->entryfunc = ftrace_pids_enabled(op) ?
                                fgraph_pid_func : gops->saved_func;
                        if (ftrace_graph_active == 1)
                                static_call_update(fgraph_func, gops->entryfunc);
                }
        }
}
#endif

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

        ret_stack_list = kcalloc(FTRACE_RETSTACK_ALLOC_SIZE,
                                 sizeof(*ret_stack_list), GFP_KERNEL);

        if (!ret_stack_list)
                return -ENOMEM;

        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;
}

static void init_task_vars(int idx)
{
        struct task_struct *g, *t;
        int cpu;

        for_each_online_cpu(cpu) {
                if (idle_task(cpu)->ret_stack)
                        ret_stack_set_task_var(idle_task(cpu), idx, 0);
        }

        read_lock(&tasklist_lock);
        for_each_process_thread(g, t) {
                if (t->ret_stack)
                        ret_stack_set_task_var(t, idx, 0);
        }
        read_unlock(&tasklist_lock);
}

static void ftrace_graph_enable_direct(bool enable_branch, struct fgraph_ops *gops)
{
        trace_func_graph_ent_t func = NULL;
        trace_func_graph_ret_t retfunc = NULL;
        int i;

        if (gops) {
                func = gops->entryfunc;
                retfunc = gops->retfunc;
                fgraph_direct_gops = gops;
        } else {
                for_each_set_bit(i, &fgraph_array_bitmask,
                                 sizeof(fgraph_array_bitmask) * BITS_PER_BYTE) {
                        func = fgraph_array[i]->entryfunc;
                        retfunc = fgraph_array[i]->retfunc;
                        fgraph_direct_gops = fgraph_array[i];
                }
        }
        if (WARN_ON_ONCE(!func))
                return;

        static_call_update(fgraph_func, func);
        static_call_update(fgraph_retfunc, retfunc);
        if (enable_branch)
                static_branch_disable(&fgraph_do_direct);
}

static void ftrace_graph_disable_direct(bool disable_branch)
{
        if (disable_branch)
                static_branch_disable(&fgraph_do_direct);
        static_call_update(fgraph_func, ftrace_graph_entry_stub);
        static_call_update(fgraph_retfunc, ftrace_graph_ret_stub);
        fgraph_direct_gops = &fgraph_stub;
}

/* The cpu_boot init_task->ret_stack will never be freed */
static int fgraph_cpu_init(unsigned int cpu)
{
        if (!idle_task(cpu)->ret_stack)
                ftrace_graph_init_idle_task(idle_task(cpu), cpu);
        return 0;
}

int register_ftrace_graph(struct fgraph_ops *gops)
{
        static bool fgraph_initialized;
        int command = 0;
        int ret = 0;
        int i = -1;

        guard(mutex)(&ftrace_lock);

        if (!fgraph_stack_cachep) {
                fgraph_stack_cachep = kmem_cache_create("fgraph_stack",
                                                        SHADOW_STACK_SIZE,
                                                        SHADOW_STACK_SIZE, 0, NULL);
                if (!fgraph_stack_cachep)
                        return -ENOMEM;
        }

        if (!fgraph_initialized) {
                ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "fgraph:online",
                                        fgraph_cpu_init, NULL);
                if (ret < 0) {
                        pr_warn("fgraph: Error to init cpu hotplug support\n");
                        return ret;
                }
                fgraph_initialized = true;
                ret = 0;
        }

        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;
                fgraph_lru_init();
        }

        i = fgraph_lru_alloc_index();
        if (i < 0 || WARN_ON_ONCE(fgraph_array[i] != &fgraph_stub))
                return -ENOSPC;
        gops->idx = i;

        ftrace_graph_active++;

        if (ftrace_graph_active == 2)
                ftrace_graph_disable_direct(true);

        if (ftrace_graph_active == 1) {
                ftrace_graph_enable_direct(false, gops);
                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;
        } else {
                init_task_vars(gops->idx);
        }
        /* Always save the function, and reset at unregistering */
        gops->saved_func = gops->entryfunc;

        ret = ftrace_startup_subops(&graph_ops, &gops->ops, command);
        if (!ret)
                fgraph_array[i] = gops;

error:
        if (ret) {
                ftrace_graph_active--;
                gops->saved_func = NULL;
                fgraph_lru_release_index(i);
        }
        return ret;
}

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

        guard(mutex)(&ftrace_lock);

        if (unlikely(!ftrace_graph_active))
                return;

        if (unlikely(gops->idx < 0 || gops->idx >= FGRAPH_ARRAY_SIZE ||
                     fgraph_array[gops->idx] != gops))
                return;

        if (fgraph_lru_release_index(gops->idx) < 0)
                return;

        fgraph_array[gops->idx] = &fgraph_stub;

        ftrace_graph_active--;

        if (!ftrace_graph_active)
                command = FTRACE_STOP_FUNC_RET;

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

        if (ftrace_graph_active == 1)
                ftrace_graph_enable_direct(true, NULL);
        else if (!ftrace_graph_active)
                ftrace_graph_disable_direct(false);

        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);
        }
        gops->saved_func = NULL;
}