[PATCH 1/6] : bug fix, remove partial zero out
Lai Jiangshan
field by field directly when need.
partial-zero-out for struct trace_iterator exists when ftrace
was first introduced into mainline kernel. But in this few years,
the code of ftrace is changed a lot, and:
1) partial-zero-out for struct trace_iterator has a bug now,
cpumask_var_t started should not be zeroed out.
2) I viewed the codes and found that fields below
"/* The below is zeroed out in pipe_read */"
don't need to be zeroed out or initialized now.
So, we remove the code of "partial zero out"
Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com>
---
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 3ca9485..c6d0e1a 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -54,7 +54,6 @@ struct trace_iterator {
struct ring_buffer_iter *buffer_iter[NR_CPUS];
unsigned long iter_flags;
- /* The below is zeroed out in pipe_read */
struct trace_seq seq;
struct trace_entry *ent;
int leftover;
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5314c90..27fecf8 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3124,12 +3124,6 @@ waitagain:
if (cnt >= PAGE_SIZE)
cnt = PAGE_SIZE - 1;
- /* reset all but tr, trace, and overruns */
- memset(&iter->seq, 0,
- sizeof(struct trace_iterator) -
- offsetof(struct trace_iterator, seq));
- iter->pos = -1;
-
trace_event_read_lock();
trace_access_lock(iter->cpu_file);
while (find_next_entry_inc(iter) != NULL) {
@@ -4398,12 +4392,7 @@ static void __ftrace_dump(bool disable_tracing)
cnt++;
- /* reset all but tr, trace, and overruns */
- memset(&iter.seq, 0,
- sizeof(struct trace_iterator) -
- offsetof(struct trace_iterator, seq));
iter.iter_flags |= TRACE_FILE_LAT_FMT;
- iter.pos = -1;
if (find_next_entry_inc(&iter) != NULL) {
int ret;
--
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Frederic Weisbecker
I'm not sure exaclty why we needed to zero the seq here.
We already reset it in trace_seq_init().
We might do it again on waitagain. I lost track how we could
ever need to goto waitagain. It was about a tricky bug to fix
but I'm don't remember exactly the details.
That said, if trace_seq_to_user returns -EBUSY, we
re-init the seq buffer, so it should be fine I guess.
But concerning the need of setting iter->pos to -1, I'm not
sure we need to remove it. Shouldn't it be set to 0 btw?
Steve?
Lai Jiangshan
Yes, -EBUSY is strange here.
but any way, trace_seq_init() is called.
>
> But concerning the need of setting iter->pos to -1, I'm not
> sure we need to remove it. Shouldn't it be set to 0 btw?
>
->pos is not used here, ->idx is just increased here,
so we don't need to initialize them.
Frederic Weisbecker
Ok.