Messages in this thread Patch in this message | | | Date | Sat, 15 Jul 2023 10:12:14 -0400 | From | Steven Rostedt <> | Subject | [PATCH v2 1/2] tracing: Remove unnecessary copying of tr->current_trace |
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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
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