Commit-ID: 03889384cee7a198a79447c1ea6aca2c8e54d155
Gitweb: http://git.kernel.org/tip/03889384cee7a198a79447c1ea6aca2c8e54d155
Author: Steven Rostedt <srostedt@xxxxxxxxxx>
AuthorDate: Fri, 11 Dec 2009 09:48:22 -0500
Committer: Steven Rostedt <rostedt@xxxxxxxxxxx>
CommitDate: Fri, 11 Dec 2009 10:38:47 -0500
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@xxxxxxxxxxx>
---
include/linux/kernel.h | 2 ++
kernel/trace/trace.c | 16 ++++++++++++++++
2 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3fa4c59..5ad4199 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -492,6 +492,8 @@ extern int
__trace_printk(unsigned long ip, const char *fmt, ...)
__attribute__ ((format (printf, 2, 3)));
+extern void trace_dump_stack(void);
+
/*
* The double __builtin_constant_p is because gcc will give us an error
* if we try to allocate the static variable to fmt if it is not a
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 88bd9ae..f531301 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)
{
--
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