linux/kernel/trace/trace_branch.c
Steven Rostedt (Red Hat) 6224beb12e tracing: Have branch tracer use recursive field of task struct
Fengguang Wu's tests triggered a bug in the branch tracer's start up
test when CONFIG_DEBUG_PREEMPT set. This was because that config
adds some debug logic in the per cpu field, which calls back into
the branch tracer.

The branch tracer has its own recursive checks, but uses a per cpu
variable to implement it. If retrieving the per cpu variable calls
back into the branch tracer, you can see how things will break.

Instead of using a per cpu variable, use the trace_recursion field
of the current task struct. Simply set a bit when entering the
branch tracing and clear it when leaving. If the bit is set on
entry, just don't do the tracing.

There's also the case with lockdep, as the local_irq_save() called
before the recursion can also trigger code that can call back into
the function. Changing that to a raw_local_irq_save() will protect
that as well.

This prevents the recursion and the inevitable crash that follows.

Link: http://lkml.kernel.org/r/20150630141803.GA28071@wfg-t540p.sh.intel.com

Cc: stable@vger.kernel.org # 3.10+
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2015-07-08 11:53:45 -04:00

415 lines
9.1 KiB
C

/*
* unlikely profiler
*
* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
*/
#include <linux/kallsyms.h>
#include <linux/seq_file.h>
#include <linux/spinlock.h>
#include <linux/irqflags.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ftrace.h>
#include <linux/hash.h>
#include <linux/fs.h>
#include <asm/local.h>
#include "trace.h"
#include "trace_stat.h"
#include "trace_output.h"
#ifdef CONFIG_BRANCH_TRACER
static struct tracer branch_trace;
static int branch_tracing_enabled __read_mostly;
static DEFINE_MUTEX(branch_tracing_mutex);
static struct trace_array *branch_tracer;
static void
probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
{
struct trace_event_call *call = &event_branch;
struct trace_array *tr = branch_tracer;
struct trace_array_cpu *data;
struct ring_buffer_event *event;
struct trace_branch *entry;
struct ring_buffer *buffer;
unsigned long flags;
int pc;
const char *p;
if (current->trace_recursion & TRACE_BRANCH_BIT)
return;
/*
* I would love to save just the ftrace_likely_data pointer, but
* this code can also be used by modules. Ugly things can happen
* if the module is unloaded, and then we go and read the
* pointer. This is slower, but much safer.
*/
if (unlikely(!tr))
return;
raw_local_irq_save(flags);
current->trace_recursion |= TRACE_BRANCH_BIT;
data = this_cpu_ptr(tr->trace_buffer.data);
if (atomic_read(&data->disabled))
goto out;
pc = preempt_count();
buffer = tr->trace_buffer.buffer;
event = trace_buffer_lock_reserve(buffer, TRACE_BRANCH,
sizeof(*entry), flags, pc);
if (!event)
goto out;
entry = ring_buffer_event_data(event);
/* Strip off the path, only save the file */
p = f->file + strlen(f->file);
while (p >= f->file && *p != '/')
p--;
p++;
strncpy(entry->func, f->func, TRACE_FUNC_SIZE);
strncpy(entry->file, p, TRACE_FILE_SIZE);
entry->func[TRACE_FUNC_SIZE] = 0;
entry->file[TRACE_FILE_SIZE] = 0;
entry->line = f->line;
entry->correct = val == expect;
if (!call_filter_check_discard(call, entry, buffer, event))
__buffer_unlock_commit(buffer, event);
out:
current->trace_recursion &= ~TRACE_BRANCH_BIT;
raw_local_irq_restore(flags);
}
static inline
void trace_likely_condition(struct ftrace_branch_data *f, int val, int expect)
{
if (!branch_tracing_enabled)
return;
probe_likely_condition(f, val, expect);
}
int enable_branch_tracing(struct trace_array *tr)
{
mutex_lock(&branch_tracing_mutex);
branch_tracer = tr;
/*
* Must be seen before enabling. The reader is a condition
* where we do not need a matching rmb()
*/
smp_wmb();
branch_tracing_enabled++;
mutex_unlock(&branch_tracing_mutex);
return 0;
}
void disable_branch_tracing(void)
{
mutex_lock(&branch_tracing_mutex);
if (!branch_tracing_enabled)
goto out_unlock;
branch_tracing_enabled--;
out_unlock:
mutex_unlock(&branch_tracing_mutex);
}
static void start_branch_trace(struct trace_array *tr)
{
enable_branch_tracing(tr);
}
static void stop_branch_trace(struct trace_array *tr)
{
disable_branch_tracing();
}
static int branch_trace_init(struct trace_array *tr)
{
start_branch_trace(tr);
return 0;
}
static void branch_trace_reset(struct trace_array *tr)
{
stop_branch_trace(tr);
}
static enum print_line_t trace_branch_print(struct trace_iterator *iter,
int flags, struct trace_event *event)
{
struct trace_branch *field;
trace_assign_type(field, iter->ent);
trace_seq_printf(&iter->seq, "[%s] %s:%s:%d\n",
field->correct ? " ok " : " MISS ",
field->func,
field->file,
field->line);
return trace_handle_return(&iter->seq);
}
static void branch_print_header(struct seq_file *s)
{
seq_puts(s, "# TASK-PID CPU# TIMESTAMP CORRECT"
" FUNC:FILE:LINE\n"
"# | | | | | "
" |\n");
}
static struct trace_event_functions trace_branch_funcs = {
.trace = trace_branch_print,
};
static struct trace_event trace_branch_event = {
.type = TRACE_BRANCH,
.funcs = &trace_branch_funcs,
};
static struct tracer branch_trace __read_mostly =
{
.name = "branch",
.init = branch_trace_init,
.reset = branch_trace_reset,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_branch,
#endif /* CONFIG_FTRACE_SELFTEST */
.print_header = branch_print_header,
};
__init static int init_branch_tracer(void)
{
int ret;
ret = register_trace_event(&trace_branch_event);
if (!ret) {
printk(KERN_WARNING "Warning: could not register "
"branch events\n");
return 1;
}
return register_tracer(&branch_trace);
}
core_initcall(init_branch_tracer);
#else
static inline
void trace_likely_condition(struct ftrace_branch_data *f, int val, int expect)
{
}
#endif /* CONFIG_BRANCH_TRACER */
void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect)
{
/*
* I would love to have a trace point here instead, but the
* trace point code is so inundated with unlikely and likely
* conditions that the recursive nightmare that exists is too
* much to try to get working. At least for now.
*/
trace_likely_condition(f, val, expect);
/* FIXME: Make this atomic! */
if (val == expect)
f->correct++;
else
f->incorrect++;
}
EXPORT_SYMBOL(ftrace_likely_update);
extern unsigned long __start_annotated_branch_profile[];
extern unsigned long __stop_annotated_branch_profile[];
static int annotated_branch_stat_headers(struct seq_file *m)
{
seq_puts(m, " correct incorrect % "
" Function "
" File Line\n"
" ------- --------- - "
" -------- "
" ---- ----\n");
return 0;
}
static inline long get_incorrect_percent(struct ftrace_branch_data *p)
{
long percent;
if (p->correct) {
percent = p->incorrect * 100;
percent /= p->correct + p->incorrect;
} else
percent = p->incorrect ? 100 : -1;
return percent;
}
static int branch_stat_show(struct seq_file *m, void *v)
{
struct ftrace_branch_data *p = v;
const char *f;
long percent;
/* Only print the file, not the path */
f = p->file + strlen(p->file);
while (f >= p->file && *f != '/')
f--;
f++;
/*
* The miss is overlayed on correct, and hit on incorrect.
*/
percent = get_incorrect_percent(p);
seq_printf(m, "%8lu %8lu ", p->correct, p->incorrect);
if (percent < 0)
seq_puts(m, " X ");
else
seq_printf(m, "%3ld ", percent);
seq_printf(m, "%-30.30s %-20.20s %d\n", p->func, f, p->line);
return 0;
}
static void *annotated_branch_stat_start(struct tracer_stat *trace)
{
return __start_annotated_branch_profile;
}
static void *
annotated_branch_stat_next(void *v, int idx)
{
struct ftrace_branch_data *p = v;
++p;
if ((void *)p >= (void *)__stop_annotated_branch_profile)
return NULL;
return p;
}
static int annotated_branch_stat_cmp(void *p1, void *p2)
{
struct ftrace_branch_data *a = p1;
struct ftrace_branch_data *b = p2;
long percent_a, percent_b;
percent_a = get_incorrect_percent(a);
percent_b = get_incorrect_percent(b);
if (percent_a < percent_b)
return -1;
if (percent_a > percent_b)
return 1;
if (a->incorrect < b->incorrect)
return -1;
if (a->incorrect > b->incorrect)
return 1;
/*
* Since the above shows worse (incorrect) cases
* first, we continue that by showing best (correct)
* cases last.
*/
if (a->correct > b->correct)
return -1;
if (a->correct < b->correct)
return 1;
return 0;
}
static struct tracer_stat annotated_branch_stats = {
.name = "branch_annotated",
.stat_start = annotated_branch_stat_start,
.stat_next = annotated_branch_stat_next,
.stat_cmp = annotated_branch_stat_cmp,
.stat_headers = annotated_branch_stat_headers,
.stat_show = branch_stat_show
};
__init static int init_annotated_branch_stats(void)
{
int ret;
ret = register_stat_tracer(&annotated_branch_stats);
if (!ret) {
printk(KERN_WARNING "Warning: could not register "
"annotated branches stats\n");
return 1;
}
return 0;
}
fs_initcall(init_annotated_branch_stats);
#ifdef CONFIG_PROFILE_ALL_BRANCHES
extern unsigned long __start_branch_profile[];
extern unsigned long __stop_branch_profile[];
static int all_branch_stat_headers(struct seq_file *m)
{
seq_puts(m, " miss hit % "
" Function "
" File Line\n"
" ------- --------- - "
" -------- "
" ---- ----\n");
return 0;
}
static void *all_branch_stat_start(struct tracer_stat *trace)
{
return __start_branch_profile;
}
static void *
all_branch_stat_next(void *v, int idx)
{
struct ftrace_branch_data *p = v;
++p;
if ((void *)p >= (void *)__stop_branch_profile)
return NULL;
return p;
}
static struct tracer_stat all_branch_stats = {
.name = "branch_all",
.stat_start = all_branch_stat_start,
.stat_next = all_branch_stat_next,
.stat_headers = all_branch_stat_headers,
.stat_show = branch_stat_show
};
__init static int all_annotated_branch_stats(void)
{
int ret;
ret = register_stat_tracer(&all_branch_stats);
if (!ret) {
printk(KERN_WARNING "Warning: could not register "
"all branches stats\n");
return 1;
}
return 0;
}
fs_initcall(all_annotated_branch_stats);
#endif /* CONFIG_PROFILE_ALL_BRANCHES */