[PATCH] ftrace: fix setting of pos in read_pipe

[PATCH] ftrace: fix setting of pos in read_pipe

[Steven Rostedt]

In resetting the iterator in read_pipe, the reset of pos was
postitioned in the wrong location with respect to the memset
operation. The current code sets pos, incorrectly, to zero.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
 kernel/trace/trace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-sched-devel.git/kernel/trace/trace.c
===================================================================
--- linux-sched-devel.git.orig/kernel/trace/trace.c	2008-04-22 10:41:58.000000000 -0400
+++ linux-sched-devel.git/kernel/trace/trace.c	2008-04-22 10:42:41.000000000 -0400
@@ -2500,10 +2500,10 @@ tracing_read_pipe(struct file *filp, cha
 		cnt = PAGE_SIZE - 1;

 	/* reset all but tr, trace, and overruns */
-	iter->pos = -1;
 	memset(&iter->seq, 0,
 	       sizeof(struct trace_iterator) -
 	       offsetof(struct trace_iterator, seq));
+	iter->pos = -1;

 	/*
 	 * We need to stop all tracing on all CPUS to read the

Re: [PATCH] ftrace: fix setting of pos in read_pipe

[Ingo Molnar]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> In resetting the iterator in read_pipe, the reset of pos was 
> postitioned in the wrong location with respect to the memset 
> operation. The current code sets pos, incorrectly, to zero.

applied - but what is missing from your changelog is effects of this 
bug. When testers check lkml they might be interested in that 
information. Is the result of this bug an incorrect trace_pipe output? 
(double entries, or missed entries?)

	Ingo

Re: [PATCH] ftrace: fix setting of pos in read_pipe

[Steven Rostedt]

On Wed, 23 Apr 2008, Ingo Molnar wrote:
> applied - but what is missing from your changelog is effects of this
> bug. When testers check lkml they might be interested in that
> information. Is the result of this bug an incorrect trace_pipe output?
> (double entries, or missed entries?)

Actually, I'm not really sure what the error would be. Could be double
entries or missing entries, or infinite output. I notice the bug via code
review not tests. I could run it with the buggy code and see what the
symptoms are.

-- Steve