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Date: Wed, 26 Jun 2013 23:01:09 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Dave Jones <davej@...hat.com>
Cc: Oleg Nesterov <oleg@...hat.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Linux Kernel <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Andrey Vagin <avagin@...nvz.org>
Subject: Re: frequent softlockups with 3.10rc6.
On Wed, 2013-06-26 at 16:00 -0400, Dave Jones wrote:
> On Wed, Jun 26, 2013 at 03:52:15PM -0400, Steven Rostedt wrote:
> Yeah, that's what I meant by "this patch".
> To reduce ambiguity, I mean the one below.. There wasn't another patch
> that I missed right ?
>
On other patch, but I've found issues with the patch I sent you. This
seems to pass my initial tests, and I'm working to get this into 3.11.
This is still a beta patch.
-- Steve
Index: linux-trace.git/kernel/trace/trace.c
===================================================================
--- linux-trace.git.orig/kernel/trace/trace.c
+++ linux-trace.git/kernel/trace/trace.c
@@ -217,7 +217,13 @@ cycle_t ftrace_now(int cpu)
int tracing_is_enabled(void)
{
- return tracing_is_on();
+ /*
+ * For quick access (irqsoff uses this in fast path), just
+ * return the mirror variable of the state of the ring buffer.
+ * It's a little racy, but we don't really care.
+ */
+ smp_rmb();
+ return !global_trace.buffer_disabled;
}
/*
@@ -330,6 +336,23 @@ unsigned long trace_flags = TRACE_ITER_P
TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION;
+void tracer_tracing_on(struct trace_array *tr)
+{
+ if (tr->trace_buffer.buffer)
+ ring_buffer_record_on(tr->trace_buffer.buffer);
+ /*
+ * This flag is looked at when buffers haven't been allocated
+ * yet, or by some tracers (like irqsoff), that just want to
+ * know if the ring buffer has been disabled, but it can handle
+ * races of where it gets disabled but we still do a record.
+ * As the check is in the fast path of the tracers, it is more
+ * important to be fast than accurate.
+ */
+ tr->buffer_disabled = 0;
+ /* Make the flag seen by readers */
+ smp_wmb();
+}
+
/**
* tracing_on - enable tracing buffers
*
@@ -338,15 +361,7 @@ unsigned long trace_flags = TRACE_ITER_P
*/
void tracing_on(void)
{
- if (global_trace.trace_buffer.buffer)
- ring_buffer_record_on(global_trace.trace_buffer.buffer);
- /*
- * This flag is only looked at when buffers haven't been
- * allocated yet. We don't really care about the race
- * between setting this flag and actually turning
- * on the buffer.
- */
- global_trace.buffer_disabled = 0;
+ tracer_tracing_on(&global_trace);
}
EXPORT_SYMBOL_GPL(tracing_on);
@@ -540,6 +555,23 @@ void tracing_snapshot_alloc(void)
EXPORT_SYMBOL_GPL(tracing_snapshot_alloc);
#endif /* CONFIG_TRACER_SNAPSHOT */
+void tracer_tracing_off(struct trace_array *tr)
+{
+ if (tr->trace_buffer.buffer)
+ ring_buffer_record_off(tr->trace_buffer.buffer);
+ /*
+ * This flag is looked at when buffers haven't been allocated
+ * yet, or by some tracers (like irqsoff), that just want to
+ * know if the ring buffer has been disabled, but it can handle
+ * races of where it gets disabled but we still do a record.
+ * As the check is in the fast path of the tracers, it is more
+ * important to be fast than accurate.
+ */
+ tr->buffer_disabled = 1;
+ /* Make the flag seen by readers */
+ smp_wmb();
+}
+
/**
* tracing_off - turn off tracing buffers
*
@@ -550,26 +582,23 @@ EXPORT_SYMBOL_GPL(tracing_snapshot_alloc
*/
void tracing_off(void)
{
- if (global_trace.trace_buffer.buffer)
- ring_buffer_record_off(global_trace.trace_buffer.buffer);
- /*
- * This flag is only looked at when buffers haven't been
- * allocated yet. We don't really care about the race
- * between setting this flag and actually turning
- * on the buffer.
- */
- global_trace.buffer_disabled = 1;
+ tracer_tracing_off(&global_trace);
}
EXPORT_SYMBOL_GPL(tracing_off);
+int tracer_tracing_is_on(struct trace_array *tr)
+{
+ if (tr->trace_buffer.buffer)
+ return ring_buffer_record_is_on(tr->trace_buffer.buffer);
+ return !tr->buffer_disabled;
+}
+
/**
* tracing_is_on - show state of ring buffers enabled
*/
int tracing_is_on(void)
{
- if (global_trace.trace_buffer.buffer)
- return ring_buffer_record_is_on(global_trace.trace_buffer.buffer);
- return !global_trace.buffer_disabled;
+ return tracer_tracing_is_on(&global_trace);
}
EXPORT_SYMBOL_GPL(tracing_is_on);
@@ -3939,7 +3968,7 @@ static int tracing_wait_pipe(struct file
*
* iter->pos will be 0 if we haven't read anything.
*/
- if (!tracing_is_enabled() && iter->pos)
+ if (!tracing_is_on() && iter->pos)
break;
}
@@ -5612,15 +5641,10 @@ rb_simple_read(struct file *filp, char _
size_t cnt, loff_t *ppos)
{
struct trace_array *tr = filp->private_data;
- struct ring_buffer *buffer = tr->trace_buffer.buffer;
char buf[64];
int r;
- if (buffer)
- r = ring_buffer_record_is_on(buffer);
- else
- r = 0;
-
+ r = tracer_tracing_is_on(tr);
r = sprintf(buf, "%d\n", r);
return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
@@ -5642,11 +5666,11 @@ rb_simple_write(struct file *filp, const
if (buffer) {
mutex_lock(&trace_types_lock);
if (val) {
- ring_buffer_record_on(buffer);
+ tracer_tracing_on(tr);
if (tr->current_trace->start)
tr->current_trace->start(tr);
} else {
- ring_buffer_record_off(buffer);
+ tracer_tracing_off(tr);
if (tr->current_trace->stop)
tr->current_trace->stop(tr);
}
Index: linux-trace.git/kernel/trace/trace_irqsoff.c
===================================================================
--- linux-trace.git.orig/kernel/trace/trace_irqsoff.c
+++ linux-trace.git/kernel/trace/trace_irqsoff.c
@@ -373,7 +373,7 @@ start_critical_timing(unsigned long ip,
struct trace_array_cpu *data;
unsigned long flags;
- if (likely(!tracer_enabled))
+ if (!tracer_enabled || !tracing_is_enabled())
return;
cpu = raw_smp_processor_id();
@@ -416,7 +416,7 @@ stop_critical_timing(unsigned long ip, u
else
return;
- if (!tracer_enabled)
+ if (!tracer_enabled || !tracing_is_enabled())
return;
data = per_cpu_ptr(tr->trace_buffer.data, cpu);
--
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