Re: [PATCH 5.5 150/367] tracing: Annotate ftrace_graph_hash pointer with __rcu

[Joel Fernandes]

On Mon, Feb 10, 2020 at 4:40 AM Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Amol Grover <frextrite@xxxxxxxxx>
>
> [ Upstream commit 24a9729f831462b1d9d61dc85ecc91c59037243f ]

Amol, can you send a follow-up patch to annotate
ftrace_graph_notrace_hash as well?

- Joel

>
> Fix following instances of sparse error
> kernel/trace/ftrace.c:5664:29: error: incompatible types in comparison
> kernel/trace/ftrace.c:5785:21: error: incompatible types in comparison
> kernel/trace/ftrace.c:5864:36: error: incompatible types in comparison
> kernel/trace/ftrace.c:5866:25: error: incompatible types in comparison
>
> Use rcu_dereference_protected to access the __rcu annotated pointer.
>
> Link: http://lkml.kernel.org/r/20200201072703.17330-1-frextrite@xxxxxxxxx
>
> Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Amol Grover <frextrite@xxxxxxxxx>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  kernel/trace/ftrace.c | 2 +-
>  kernel/trace/trace.h  | 9 ++++++---
>  2 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 9bf1f2cd515ef..959ded08dc13f 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5596,7 +5596,7 @@ static const struct file_operations ftrace_notrace_fops = {
>
>  static DEFINE_MUTEX(graph_lock);
>
> -struct ftrace_hash *ftrace_graph_hash = EMPTY_HASH;
> +struct ftrace_hash __rcu *ftrace_graph_hash = EMPTY_HASH;
>  struct ftrace_hash *ftrace_graph_notrace_hash = EMPTY_HASH;
>
>  enum graph_filter_type {
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 63bf60f793987..97dad33260208 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -950,22 +950,25 @@ extern void __trace_graph_return(struct trace_array *tr,
>                                  unsigned long flags, int pc);
>
>  #ifdef CONFIG_DYNAMIC_FTRACE
> -extern struct ftrace_hash *ftrace_graph_hash;
> +extern struct ftrace_hash __rcu *ftrace_graph_hash;
>  extern struct ftrace_hash *ftrace_graph_notrace_hash;
>
>  static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace)
>  {
>         unsigned long addr = trace->func;
>         int ret = 0;
> +       struct ftrace_hash *hash;
>
>         preempt_disable_notrace();
>
> -       if (ftrace_hash_empty(ftrace_graph_hash)) {
> +       hash = rcu_dereference_protected(ftrace_graph_hash, !preemptible());
> +
> +       if (ftrace_hash_empty(hash)) {
>                 ret = 1;
>                 goto out;
>         }
>
> -       if (ftrace_lookup_ip(ftrace_graph_hash, addr)) {
> +       if (ftrace_lookup_ip(hash, addr)) {
>
>                 /*
>                  * This needs to be cleared on the return functions
> --
> 2.20.1
>
>
>