lkml.org 
[lkml]   [2011]   [Apr]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 3/6] tracing: Avoid soft lockup in trace_pipe
From: Jiri Olsa <jolsa@redhat.com>

running following commands:

# enable the binary option
echo 1 > ./options/bin
# disable context info option
echo 0 > ./options/context-info
# tracing only events
echo 1 > ./events/enable
cat trace_pipe
plus forcing system to generate many tracing events,
is causing lockup (in NON preemptive kernels) inside
tracing_read_pipe function.

The issue is also easily reproduced by running ltp stress test.
(ftrace_stress_test.sh)

The reasons are:
- bin/hex/raw output functions for events are set to
trace_nop_print function, which prints nothing and
returns TRACE_TYPE_HANDLED value
- LOST EVENT trace do not handle trace_seq overflow

These reasons force the while loop in tracing_read_pipe
function never to break.

The attached patch fixies handling of lost event trace, and
changes trace_nop_print to print minimal info, which is needed
for the correct tracing_read_pipe processing.

v2 changes:
- omit the cond_resched changes by trace_nop_print changes
- WARN changed to WARN_ONCE and added info to be able
to find out the culprit

v3 changes:
- make more accurate patch comment

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
LKML-Reference: <20110325110518.GC1922@jolsa.brq.redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace.c | 15 ++++++++++++---
kernel/trace/trace_output.c | 3 +++
2 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9541c27..5af42f4 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2013,9 +2013,10 @@ enum print_line_t print_trace_line(struct trace_iterator *iter)
{
enum print_line_t ret;

- if (iter->lost_events)
- trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n",
- iter->cpu, iter->lost_events);
+ if (iter->lost_events &&
+ !trace_seq_printf(&iter->seq, "CPU:%d [LOST %lu EVENTS]\n",
+ iter->cpu, iter->lost_events))
+ return TRACE_TYPE_PARTIAL_LINE;

if (iter->trace && iter->trace->print_line) {
ret = iter->trace->print_line(iter);
@@ -3229,6 +3230,14 @@ waitagain:

if (iter->seq.len >= cnt)
break;
+
+ /*
+ * Setting the full flag means we reached the trace_seq buffer
+ * size and we should leave by partial output condition above.
+ * One of the trace_seq_* functions is not used properly.
+ */
+ WARN_ONCE(iter->seq.full, "full flag set for trace type %d",
+ iter->ent->type);
}
trace_access_unlock(iter->cpu_file);
trace_event_read_unlock();
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 456be90..cf535cc 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -830,6 +830,9 @@ EXPORT_SYMBOL_GPL(unregister_ftrace_event);
enum print_line_t trace_nop_print(struct trace_iterator *iter, int flags,
struct trace_event *event)
{
+ if (!trace_seq_printf(&iter->seq, "type: %d\n", iter->ent->type))
+ return TRACE_TYPE_PARTIAL_LINE;
+
return TRACE_TYPE_HANDLED;
}

--
1.7.2.3



\
 
 \ /
  Last update: 2011-04-04 21:21    [from the cache]
©2003-2011 Jasper Spaans