linux/kernel/trace/trace_hw_branches.c
Ingo Molnar 2d542cf342 tracing/hw-branch-tracing: convert bts-tracer mutex to a spinlock
Impact: fix CPU hotplug lockup

bts_hotcpu_handler() is called with irqs disabled, so using mutex_lock()
is a no-no.

All the BTS codepaths here are atomic (they do not schedule), so using
a spinlock is the right solution.

Cc: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-25 09:16:01 +01:00

303 lines
6.4 KiB
C

/*
* h/w branch tracer for x86 based on bts
*
* Copyright (C) 2008-2009 Intel Corporation.
* Markus Metzger <markus.t.metzger@gmail.com>, 2008-2009
*/
#include <linux/spinlock.h>
#include <linux/kallsyms.h>
#include <linux/debugfs.h>
#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/fs.h>
#include <asm/ds.h>
#include "trace.h"
#include "trace_output.h"
#define SIZEOF_BTS (1 << 13)
/*
* The tracer lock protects the below per-cpu tracer array.
* It needs to be held to:
* - start tracing on all cpus
* - stop tracing on all cpus
* - start tracing on a single hotplug cpu
* - stop tracing on a single hotplug cpu
* - read the trace from all cpus
* - read the trace from a single cpu
*/
static DEFINE_SPINLOCK(bts_tracer_lock);
static DEFINE_PER_CPU(struct bts_tracer *, tracer);
static DEFINE_PER_CPU(unsigned char[SIZEOF_BTS], buffer);
#define this_tracer per_cpu(tracer, smp_processor_id())
#define this_buffer per_cpu(buffer, smp_processor_id())
static int __read_mostly trace_hw_branches_enabled;
static struct trace_array *hw_branch_trace __read_mostly;
/*
* Start tracing on the current cpu.
* The argument is ignored.
*
* pre: bts_tracer_lock must be locked.
*/
static void bts_trace_start_cpu(void *arg)
{
if (this_tracer)
ds_release_bts(this_tracer);
this_tracer =
ds_request_bts(/* task = */ NULL, this_buffer, SIZEOF_BTS,
/* ovfl = */ NULL, /* th = */ (size_t)-1,
BTS_KERNEL);
if (IS_ERR(this_tracer)) {
this_tracer = NULL;
return;
}
}
static void bts_trace_start(struct trace_array *tr)
{
spin_lock(&bts_tracer_lock);
on_each_cpu(bts_trace_start_cpu, NULL, 1);
trace_hw_branches_enabled = 1;
spin_unlock(&bts_tracer_lock);
}
/*
* Stop tracing on the current cpu.
* The argument is ignored.
*
* pre: bts_tracer_lock must be locked.
*/
static void bts_trace_stop_cpu(void *arg)
{
if (this_tracer) {
ds_release_bts(this_tracer);
this_tracer = NULL;
}
}
static void bts_trace_stop(struct trace_array *tr)
{
spin_lock(&bts_tracer_lock);
trace_hw_branches_enabled = 0;
on_each_cpu(bts_trace_stop_cpu, NULL, 1);
spin_unlock(&bts_tracer_lock);
}
static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
unsigned int cpu = (unsigned long)hcpu;
spin_lock(&bts_tracer_lock);
if (!trace_hw_branches_enabled)
goto out;
switch (action) {
case CPU_ONLINE:
case CPU_DOWN_FAILED:
smp_call_function_single(cpu, bts_trace_start_cpu, NULL, 1);
break;
case CPU_DOWN_PREPARE:
smp_call_function_single(cpu, bts_trace_stop_cpu, NULL, 1);
break;
}
out:
spin_unlock(&bts_tracer_lock);
return NOTIFY_DONE;
}
static struct notifier_block bts_hotcpu_notifier __cpuinitdata = {
.notifier_call = bts_hotcpu_handler
};
static int bts_trace_init(struct trace_array *tr)
{
hw_branch_trace = tr;
bts_trace_start(tr);
return 0;
}
static void bts_trace_reset(struct trace_array *tr)
{
bts_trace_stop(tr);
}
static void bts_trace_print_header(struct seq_file *m)
{
seq_puts(m, "# CPU# TO <- FROM\n");
}
static enum print_line_t bts_trace_print_line(struct trace_iterator *iter)
{
struct trace_entry *entry = iter->ent;
struct trace_seq *seq = &iter->seq;
struct hw_branch_entry *it;
unsigned long symflags = TRACE_ITER_SYM_OFFSET;
trace_assign_type(it, entry);
if (entry->type == TRACE_HW_BRANCHES) {
if (trace_seq_printf(seq, "%4d ", iter->cpu) &&
seq_print_ip_sym(seq, it->to, symflags) &&
trace_seq_printf(seq, "\t <- ") &&
seq_print_ip_sym(seq, it->from, symflags) &&
trace_seq_printf(seq, "\n"))
return TRACE_TYPE_HANDLED;
return TRACE_TYPE_PARTIAL_LINE;;
}
return TRACE_TYPE_UNHANDLED;
}
void trace_hw_branch(u64 from, u64 to)
{
struct trace_array *tr = hw_branch_trace;
struct ring_buffer_event *event;
struct hw_branch_entry *entry;
unsigned long irq1;
int cpu;
if (unlikely(!tr))
return;
if (unlikely(!trace_hw_branches_enabled))
return;
local_irq_save(irq1);
cpu = raw_smp_processor_id();
if (atomic_inc_return(&tr->data[cpu]->disabled) != 1)
goto out;
event = trace_buffer_lock_reserve(tr, TRACE_HW_BRANCHES,
sizeof(*entry), 0, 0);
if (!event)
goto out;
entry = ring_buffer_event_data(event);
tracing_generic_entry_update(&entry->ent, 0, from);
entry->ent.type = TRACE_HW_BRANCHES;
entry->from = from;
entry->to = to;
trace_buffer_unlock_commit(tr, event, 0, 0);
out:
atomic_dec(&tr->data[cpu]->disabled);
local_irq_restore(irq1);
}
static void trace_bts_at(const struct bts_trace *trace, void *at)
{
struct bts_struct bts;
int err = 0;
WARN_ON_ONCE(!trace->read);
if (!trace->read)
return;
err = trace->read(this_tracer, at, &bts);
if (err < 0)
return;
switch (bts.qualifier) {
case BTS_BRANCH:
trace_hw_branch(bts.variant.lbr.from, bts.variant.lbr.to);
break;
}
}
/*
* Collect the trace on the current cpu and write it into the ftrace buffer.
*
* pre: bts_tracer_lock must be locked
*/
static void trace_bts_cpu(void *arg)
{
struct trace_array *tr = (struct trace_array *) arg;
const struct bts_trace *trace;
unsigned char *at;
if (unlikely(!tr))
return;
if (unlikely(atomic_read(&tr->data[raw_smp_processor_id()]->disabled)))
return;
if (unlikely(!this_tracer))
return;
ds_suspend_bts(this_tracer);
trace = ds_read_bts(this_tracer);
if (!trace)
goto out;
for (at = trace->ds.top; (void *)at < trace->ds.end;
at += trace->ds.size)
trace_bts_at(trace, at);
for (at = trace->ds.begin; (void *)at < trace->ds.top;
at += trace->ds.size)
trace_bts_at(trace, at);
out:
ds_resume_bts(this_tracer);
}
static void trace_bts_prepare(struct trace_iterator *iter)
{
spin_lock(&bts_tracer_lock);
on_each_cpu(trace_bts_cpu, iter->tr, 1);
spin_unlock(&bts_tracer_lock);
}
static void trace_bts_close(struct trace_iterator *iter)
{
tracing_reset_online_cpus(iter->tr);
}
void trace_hw_branch_oops(void)
{
spin_lock(&bts_tracer_lock);
trace_bts_cpu(hw_branch_trace);
spin_unlock(&bts_tracer_lock);
}
struct tracer bts_tracer __read_mostly =
{
.name = "hw-branch-tracer",
.init = bts_trace_init,
.reset = bts_trace_reset,
.print_header = bts_trace_print_header,
.print_line = bts_trace_print_line,
.start = bts_trace_start,
.stop = bts_trace_stop,
.open = trace_bts_prepare,
.close = trace_bts_close
};
__init static int init_bts_trace(void)
{
register_hotcpu_notifier(&bts_hotcpu_notifier);
return register_tracer(&bts_tracer);
}
device_initcall(init_bts_trace);