tracing: Remove unnecessary copying of tr->current_trace

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.

Link: https://lkml.kernel.org/r/20230715141348.135792275@goodmis.org
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f6ed6b7..5e665c3 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4189,15 +4189,9 @@ 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
@@ -4846,16 +4840,8 @@ __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;
@@ -4920,7 +4906,6 @@ __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:
@@ -5005,7 +4990,6 @@ 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);