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authorJiri Olsa <jolsa@redhat.com>2011-03-25 14:05:18 +0300
committerSteven Rostedt <rostedt@goodmis.org>2011-04-04 20:18:24 +0400
commitee5e51f51be755830f57445e268ba50e88ccbdbb (patch)
tree059d6c5843275a5ab94ae01408c1dc6dbe00b2ea /kernel/trace/trace_output.c
parent1813dc3776c22ad4b0294a6df8434b9a02c98109 (diff)
downloadlinux-ee5e51f51be755830f57445e268ba50e88ccbdbb.tar.xz
tracing: Avoid soft lockup in trace_pipe
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>
Diffstat (limited to 'kernel/trace/trace_output.c')
-rw-r--r--kernel/trace/trace_output.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 456be9063c2d..cf535ccedc86 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;
}