linux/include
Steven Rostedt 03889384ce 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>
2009-12-11 10:38:47 -05:00
..
acpi
asm-generic Merge branch 'for-2.6.33' of git://git.kernel.dk/linux-2.6-block 2009-12-08 08:19:16 -08:00
crypto
drm
keys
linux tracing: Add trace_dump_stack() 2009-12-11 10:38:47 -05:00
math-emu
media
mtd
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6 2009-12-08 07:55:01 -08:00
pcmcia Merge git://git.kernel.org/pub/scm/linux/kernel/git/brodo/pcmcia-2.6 2009-12-05 09:42:59 -08:00
rdma
rxrpc
scsi [SCSI] fix async scan add/remove race resulting in an oops 2009-11-26 09:43:39 -06:00
sound Merge branch 'topic/hda' into for-linus 2009-12-04 16:22:45 +01:00
trace Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-12-05 15:30:21 -08:00
video pxa168fb: remove useless vsync/hsync invert flag 2009-12-01 09:02:32 +08:00
xen
Kbuild