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tracing: Make tracepoint_printk a static_key 

Currently, when tracepoint_printk is set (enabled by the "tp_printk" kernel
command line), it causes trace events to print via printk(). This is a very
dangerous operation, but is useful for debugging.

The issue is, it's seldom used, but it is always checked even if it's not
enabled by the kernel command line. Instead of having this feature called by
a branch against a variable, turn that variable into a static key, and this
will remove the test and jump.

To simplify things, the functions output_printk() and
trace_event_buffer_commit() were moved from trace_events.c to trace.c.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Red Hat) 2016-11-23 15:52:45 -05:00 committed by Steven Rostedt
parent 929ddbf3ef
commit 4239174570
4 changed files with 83 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/linux/ftrace.h
View File

@ -945,6 +945,10 @@ extern int __disable_trace_on_warning;
#define INIT_TRACE_RECURSION .trace_recursion = 0,
#endif
int tracepoint_printk_sysctl(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos);
#else /* CONFIG_TRACING */
static inline void disable_trace_on_warning(void) { }
#endif /* CONFIG_TRACING */

2
kernel/sysctl.c
View File

@ -634,7 +634,7 @@ static struct ctl_table kern_table[] = {
.data = &tracepoint_printk,
.maxlen = sizeof(tracepoint_printk),
.mode = 0644,
.proc_handler = proc_dointvec,
.proc_handler = tracepoint_printk_sysctl,
},
#endif
#ifdef CONFIG_KEXEC_CORE

78
kernel/trace/trace.c
View File

@ -69,6 +69,7 @@ bool __read_mostly tracing_selftest_disabled;
/* Pipe tracepoints to printk */
struct trace_iterator *tracepoint_print_iter;
int tracepoint_printk;
static DEFINE_STATIC_KEY_FALSE(tracepoint_printk_key);
/* For tracers that don't implement custom flags */
static struct tracer_opt dummy_tracer_opt[] = {
@ -2116,6 +2117,81 @@ trace_event_buffer_lock_reserve(struct ring_buffer **current_rb,
}
EXPORT_SYMBOL_GPL(trace_event_buffer_lock_reserve);
static DEFINE_SPINLOCK(tracepoint_iter_lock);
static DEFINE_MUTEX(tracepoint_printk_mutex);
static void output_printk(struct trace_event_buffer *fbuffer)
{
struct trace_event_call *event_call;
struct trace_event *event;
unsigned long flags;
struct trace_iterator *iter = tracepoint_print_iter;
/* We should never get here if iter is NULL */
if (WARN_ON_ONCE(!iter))
return;
event_call = fbuffer->trace_file->event_call;
if (!event_call || !event_call->event.funcs ||
!event_call->event.funcs->trace)
return;
event = &fbuffer->trace_file->event_call->event;
spin_lock_irqsave(&tracepoint_iter_lock, flags);
trace_seq_init(&iter->seq);
iter->ent = fbuffer->entry;
event_call->event.funcs->trace(iter, 0, event);
trace_seq_putc(&iter->seq, 0);
printk("%s", iter->seq.buffer);
spin_unlock_irqrestore(&tracepoint_iter_lock, flags);
}
int tracepoint_printk_sysctl(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
{
int save_tracepoint_printk;
int ret;
mutex_lock(&tracepoint_printk_mutex);
save_tracepoint_printk = tracepoint_printk;
ret = proc_dointvec(table, write, buffer, lenp, ppos);
/*
* This will force exiting early, as tracepoint_printk
* is always zero when tracepoint_printk_iter is not allocated
*/
if (!tracepoint_print_iter)
tracepoint_printk = 0;
if (save_tracepoint_printk == tracepoint_printk)
goto out;
if (tracepoint_printk)
static_key_enable(&tracepoint_printk_key.key);
else
static_key_disable(&tracepoint_printk_key.key);
out:
mutex_unlock(&tracepoint_printk_mutex);
return ret;
}
void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
{
if (static_key_false(&tracepoint_printk_key.key))
output_printk(fbuffer);
event_trigger_unlock_commit(fbuffer->trace_file, fbuffer->buffer,
fbuffer->event, fbuffer->entry,
fbuffer->flags, fbuffer->pc);
}
EXPORT_SYMBOL_GPL(trace_event_buffer_commit);
void trace_buffer_unlock_commit_regs(struct trace_array *tr,
struct ring_buffer *buffer,
struct ring_buffer_event *event,
@ -7977,6 +8053,8 @@ void __init trace_init(void)
kmalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL);
if (WARN_ON(!tracepoint_print_iter))
tracepoint_printk = 0;
else
static_key_enable(&tracepoint_printk_key.key);
}
tracer_alloc_buffers();
trace_event_init();

40
kernel/trace/trace_events.c
View File

@ -283,46 +283,6 @@ void *trace_event_buffer_reserve(struct trace_event_buffer *fbuffer,
}
EXPORT_SYMBOL_GPL(trace_event_buffer_reserve);
static DEFINE_SPINLOCK(tracepoint_iter_lock);
static void output_printk(struct trace_event_buffer *fbuffer)
{
struct trace_event_call *event_call;
struct trace_event *event;
unsigned long flags;
struct trace_iterator *iter = tracepoint_print_iter;
if (!iter)
return;
event_call = fbuffer->trace_file->event_call;
if (!event_call || !event_call->event.funcs ||
!event_call->event.funcs->trace)
return;
event = &fbuffer->trace_file->event_call->event;
spin_lock_irqsave(&tracepoint_iter_lock, flags);
trace_seq_init(&iter->seq);
iter->ent = fbuffer->entry;
event_call->event.funcs->trace(iter, 0, event);
trace_seq_putc(&iter->seq, 0);
printk("%s", iter->seq.buffer);
spin_unlock_irqrestore(&tracepoint_iter_lock, flags);
}
void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
{
if (tracepoint_printk)
output_printk(fbuffer);
event_trigger_unlock_commit(fbuffer->trace_file, fbuffer->buffer,
fbuffer->event, fbuffer->entry,
fbuffer->flags, fbuffer->pc);
}
EXPORT_SYMBOL_GPL(trace_event_buffer_commit);
int trace_event_reg(struct trace_event_call *call,
enum trace_reg type, void *data)
{