[PATCH v2 1/2] tracing: Remove unnecessary copying of tr->current_trace

Steven Rostedt
2023-07-15T14:13:59Z

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The iterator allocated a descriptor to copy the current_trace. This was done
with the assumption that the function pointers might change. But this was a
false assuption, as it does not change. There's no reason to make a copy of the
current_trace and just use the pointer it points to. This removes needing to
manage freeing the descriptor. Worse yet, there's locations that the iterator
is used but does make a copy and just uses the pointer. This could cause the
actual pointer to the trace descriptor to be freed and not the allocated copy.

This is more of a clean up than a fix.

Fixes: d7350c3f45694 ("tracing/core: make the read callbacks reentrants")
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace.c | 22 +++-------------------
1 file changed, 3 insertions(+), 19 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index be847d45d81c..1c370ffbe062 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4205,15 +4205,9 @@ static void *s_start(struct seq_file *m, loff_t *pos)
loff_t l = 0;
int cpu;

- /*
- * copy the tracer to avoid using a global lock all around.
- * iter->trace is a copy of current_trace, the pointer to the
- * name may be used instead of a strcmp(), as iter->trace->name
- * will point to the same string as current_trace->name.
- */
mutex_lock(&trace_types_lock);
- if (unlikely(tr->current_trace && iter->trace->name != tr->current_trace->name))
- *iter->trace = *tr->current_trace;
+ if (unlikely(tr->current_trace != iter->trace))
+ iter->trace = tr->current_trace;
mutex_unlock(&trace_types_lock);

#ifdef CONFIG_TRACER_MAX_TRACE
@@ -4862,16 +4856,8 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
iter->fmt = NULL;
iter->fmt_size = 0;

- /*
- * We make a copy of the current tracer to avoid concurrent
- * changes on it while we are reading.
- */
mutex_lock(&trace_types_lock);
- iter->trace = kzalloc(sizeof(*iter->trace), GFP_KERNEL);
- if (!iter->trace)
- goto fail;
-
- *iter->trace = *tr->current_trace;
+ iter->trace = tr->current_trace;

if (!zalloc_cpumask_var(&iter->started, GFP_KERNEL))
goto fail;
@@ -4936,7 +4922,6 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)

fail:
mutex_unlock(&trace_types_lock);
- kfree(iter->trace);
kfree(iter->temp);
kfree(iter->buffer_iter);
release:
@@ -5021,7 +5006,6 @@ static int tracing_release(struct inode *inode, struct file *file)
free_cpumask_var(iter->started);
kfree(iter->fmt);
kfree(iter->temp);
- kfree(iter->trace);
kfree(iter->buffer_iter);
seq_release_private(inode, file);

--
2.40.1