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![Yuntao Wang](/assets/img/avatar_default.png)
Creating tracefs entries with tracefs_create_file() followed by pr_warn() is tedious and repetitive, we can use trace_create_file() to simplify this process and make the code more readable. Link: https://lkml.kernel.org/r/20220114131052.534382-1-ytcoode@gmail.com Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Signed-off-by: Yuntao Wang <ytcoode@gmail.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
233 lines
6 KiB
C
233 lines
6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/seq_file.h>
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#include <linux/kallsyms.h>
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#include <linux/module.h>
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#include <linux/ftrace.h>
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#include <linux/fs.h>
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#include "trace_output.h"
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struct recursed_functions {
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unsigned long ip;
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unsigned long parent_ip;
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};
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static struct recursed_functions recursed_functions[CONFIG_FTRACE_RECORD_RECURSION_SIZE];
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static atomic_t nr_records;
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/*
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* Cache the last found function. Yes, updates to this is racey, but
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* so is memory cache ;-)
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*/
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static unsigned long cached_function;
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void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip)
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{
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int index = 0;
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int i;
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unsigned long old;
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again:
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/* First check the last one recorded */
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if (ip == cached_function)
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return;
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i = atomic_read(&nr_records);
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/* nr_records is -1 when clearing records */
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smp_mb__after_atomic();
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if (i < 0)
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return;
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/*
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* If there's two writers and this writer comes in second,
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* the cmpxchg() below to update the ip will fail. Then this
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* writer will try again. It is possible that index will now
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* be greater than nr_records. This is because the writer
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* that succeeded has not updated the nr_records yet.
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* This writer could keep trying again until the other writer
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* updates nr_records. But if the other writer takes an
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* interrupt, and that interrupt locks up that CPU, we do
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* not want this CPU to lock up due to the recursion protection,
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* and have a bug report showing this CPU as the cause of
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* locking up the computer. To not lose this record, this
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* writer will simply use the next position to update the
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* recursed_functions, and it will update the nr_records
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* accordingly.
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*/
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if (index < i)
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index = i;
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if (index >= CONFIG_FTRACE_RECORD_RECURSION_SIZE)
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return;
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for (i = index - 1; i >= 0; i--) {
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if (recursed_functions[i].ip == ip) {
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cached_function = ip;
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return;
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}
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}
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cached_function = ip;
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/*
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* We only want to add a function if it hasn't been added before.
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* Add to the current location before incrementing the count.
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* If it fails to add, then increment the index (save in i)
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* and try again.
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*/
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old = cmpxchg(&recursed_functions[index].ip, 0, ip);
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if (old != 0) {
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/* Did something else already added this for us? */
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if (old == ip)
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return;
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/* Try the next location (use i for the next index) */
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index++;
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goto again;
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}
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recursed_functions[index].parent_ip = parent_ip;
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/*
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* It's still possible that we could race with the clearing
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* CPU0 CPU1
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* ---- ----
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* ip = func
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* nr_records = -1;
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* recursed_functions[0] = 0;
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* i = -1
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* if (i < 0)
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* nr_records = 0;
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* (new recursion detected)
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* recursed_functions[0] = func
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* cmpxchg(recursed_functions[0],
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* func, 0)
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*
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* But the worse that could happen is that we get a zero in
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* the recursed_functions array, and it's likely that "func" will
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* be recorded again.
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*/
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i = atomic_read(&nr_records);
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smp_mb__after_atomic();
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if (i < 0)
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cmpxchg(&recursed_functions[index].ip, ip, 0);
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else if (i <= index)
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atomic_cmpxchg(&nr_records, i, index + 1);
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}
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EXPORT_SYMBOL_GPL(ftrace_record_recursion);
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static DEFINE_MUTEX(recursed_function_lock);
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static struct trace_seq *tseq;
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static void *recursed_function_seq_start(struct seq_file *m, loff_t *pos)
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{
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void *ret = NULL;
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int index;
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mutex_lock(&recursed_function_lock);
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index = atomic_read(&nr_records);
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if (*pos < index) {
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ret = &recursed_functions[*pos];
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}
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tseq = kzalloc(sizeof(*tseq), GFP_KERNEL);
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if (!tseq)
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return ERR_PTR(-ENOMEM);
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trace_seq_init(tseq);
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return ret;
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}
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static void *recursed_function_seq_next(struct seq_file *m, void *v, loff_t *pos)
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{
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int index;
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int p;
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index = atomic_read(&nr_records);
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p = ++(*pos);
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return p < index ? &recursed_functions[p] : NULL;
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}
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static void recursed_function_seq_stop(struct seq_file *m, void *v)
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{
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kfree(tseq);
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mutex_unlock(&recursed_function_lock);
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}
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static int recursed_function_seq_show(struct seq_file *m, void *v)
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{
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struct recursed_functions *record = v;
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int ret = 0;
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if (record) {
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trace_seq_print_sym(tseq, record->parent_ip, true);
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trace_seq_puts(tseq, ":\t");
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trace_seq_print_sym(tseq, record->ip, true);
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trace_seq_putc(tseq, '\n');
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ret = trace_print_seq(m, tseq);
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}
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return ret;
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}
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static const struct seq_operations recursed_function_seq_ops = {
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.start = recursed_function_seq_start,
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.next = recursed_function_seq_next,
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.stop = recursed_function_seq_stop,
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.show = recursed_function_seq_show
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};
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static int recursed_function_open(struct inode *inode, struct file *file)
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{
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int ret = 0;
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mutex_lock(&recursed_function_lock);
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/* If this file was opened for write, then erase contents */
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if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
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/* disable updating records */
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atomic_set(&nr_records, -1);
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smp_mb__after_atomic();
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memset(recursed_functions, 0, sizeof(recursed_functions));
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smp_wmb();
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/* enable them again */
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atomic_set(&nr_records, 0);
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}
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if (file->f_mode & FMODE_READ)
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ret = seq_open(file, &recursed_function_seq_ops);
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mutex_unlock(&recursed_function_lock);
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return ret;
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}
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static ssize_t recursed_function_write(struct file *file,
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const char __user *buffer,
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size_t count, loff_t *ppos)
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{
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return count;
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}
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static int recursed_function_release(struct inode *inode, struct file *file)
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{
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if (file->f_mode & FMODE_READ)
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seq_release(inode, file);
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return 0;
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}
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static const struct file_operations recursed_functions_fops = {
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.open = recursed_function_open,
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.write = recursed_function_write,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = recursed_function_release,
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};
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__init static int create_recursed_functions(void)
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{
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trace_create_file("recursed_functions", TRACE_MODE_WRITE,
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NULL, NULL, &recursed_functions_fops);
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return 0;
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}
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fs_initcall(create_recursed_functions);
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