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