From: Joel Fernandes <joel@joelfernandes.org>
To: Amol Grover <frextrite@gmail.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu
Date: Mon, 3 Feb 2020 11:33:01 -0500 [thread overview]
Message-ID: <20200203163301.GB85781@google.com> (raw)
In-Reply-To: <20200201072703.17330-1-frextrite@gmail.com>
On Sat, Feb 01, 2020 at 12:57:04PM +0530, Amol Grover wrote:
> 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.
>
> Signed-off-by: Amol Grover <frextrite@gmail.com>
> ---
> 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 9bf1f2cd515e..959ded08dc13 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 63bf60f79398..97dad3326020 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());
I think you can use rcu_dereference_sched() here? That way no need to pass
!preemptible.
A preempt-disabled section is an RCU "sched flavor" section. Flavors are
consolidated in the backend, but in the front end the dereference API still
do have flavors.
thanks,
- Joel
> +
> + 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
> --
> 2.24.1
>
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next prev parent reply other threads:[~2020-02-03 16:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-01 7:27 [Linux-kernel-mentees] [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu Amol Grover
2020-02-03 16:33 ` Joel Fernandes [this message]
2020-02-04 10:02 ` Steven Rostedt
2020-02-05 1:01 ` Steven Rostedt
2020-02-05 5:26 ` Amol Grover
2020-02-05 13:11 ` Paul E. McKenney
2020-02-05 13:14 ` Steven Rostedt
2020-02-05 13:19 ` Steven Rostedt
2020-02-05 13:29 ` Paul E. McKenney
2020-02-05 22:06 ` Joel Fernandes
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