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authorSteven Rostedt <srostedt@redhat.com>2009-12-11 09:48:22 -0500
committerSteven Rostedt <rostedt@goodmis.org>2009-12-11 10:38:47 -0500
commit03889384cee7a198a79447c1ea6aca2c8e54d155 (patch)
tree66794ab12e3196c4bee4d8d020f451e8cc8a1f6d /kernel/trace
parentdd7f59435782a02ceb6d16b9ce823dd3345d75ec (diff)
downloadlinux-03889384cee7a198a79447c1ea6aca2c8e54d155.tar.bz2
tracing: Add trace_dump_stack()
I've been asked a few times about how to find out what is calling some location in the kernel. One way is to use dynamic function tracing and implement the func_stack_trace. But this only finds out who is calling a particular function. It does not tell you who is calling that function and entering a specific if conditional. I have myself implemented a quick version of trace_dump_stack() for this purpose a few times, and just needed it now. This is when I realized that this would be a good tool to have in the kernel like trace_printk(). Using trace_dump_stack() is similar to dump_stack() except that it writes to the trace buffer instead and can be used in critical locations. For example: @@ -5485,8 +5485,12 @@ need_resched_nonpreemptible: if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) { if (unlikely(signal_pending_state(prev->state, prev))) prev->state = TASK_RUNNING; - else + else { deactivate_task(rq, prev, 1); + trace_printk("Deactivating task %s:%d\n", + prev->comm, prev->pid); + trace_dump_stack(); + } switch_count = &prev->nvcsw; } Produces: <...>-3249 [001] 296.105269: schedule: Deactivating task ntpd:3249 <...>-3249 [001] 296.105270: <stack trace> => schedule => schedule_hrtimeout_range => poll_schedule_timeout => do_select => core_sys_select => sys_select => system_call_fastpath Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/trace.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 88bd9ae2a9ed..f531301b7a3b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1151,6 +1151,22 @@ void __trace_stack(struct trace_array *tr, unsigned long flags, int skip,
__ftrace_trace_stack(tr->buffer, flags, skip, pc);
}
+/**
+ * trace_dump_stack - record a stack back trace in the trace buffer
+ */
+void trace_dump_stack(void)
+{
+ unsigned long flags;
+
+ if (tracing_disabled || tracing_selftest_running)
+ return 0;
+
+ local_save_flags(flags);
+
+ /* skipping 3 traces, seems to get us at the caller of this function */
+ __ftrace_trace_stack(global_trace.buffer, flags, 3, preempt_count());
+}
+
void
ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
{