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Message-Id: <20230420155146.56099afbc6c73fc2e1065c62@kernel.org>
Date: Thu, 20 Apr 2023 15:51:46 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Yafang Shao <laoar.shao@...il.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
kafai@...com, songliubraving@...com, yhs@...com,
john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
haoluo@...gle.com, jolsa@...nel.org, rostedt@...dmis.org,
bpf@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/6] tracing: Add generic
test_recursion_try_acquire()
On Mon, 17 Apr 2023 15:47:33 +0000
Yafang Shao <laoar.shao@...il.com> wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
>
> The ftrace_test_recursion_trylock() also disables preemption. This is not
> required, but was a clean up as every place that called it also disabled
> preemption, and making the two tightly coupled appeared to make the code
> simpler.
>
> But the recursion protection can be used for other purposes that do not
> require disabling preemption. As the recursion bits are attached to the
> task_struct, it follows the task, so there's no need for preemption being
> disabled.
>
> Add test_recursion_try_acquire/release() functions to be used generically,
> and separate it from being associated with ftrace. It also removes the
> "lock" name, as there is no lock happening. Keeping the "lock" for the
> ftrace version is better, as it at least differentiates that preemption is
> being disabled (hence, "locking the CPU").
>
> Link: https://lore.kernel.org/linux-trace-kernel/20230321020103.13494-1-laoar.shao@gmail.com/
>
> Acked-by: Yafang Shao <laoar.shao@...il.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
This looks good to me.
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
> include/linux/trace_recursion.h | 47 ++++++++++++++++++++++++++++++-----------
> kernel/trace/ftrace.c | 2 ++
> 2 files changed, 37 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h
> index d48cd92..80de2ee 100644
> --- a/include/linux/trace_recursion.h
> +++ b/include/linux/trace_recursion.h
> @@ -150,9 +150,6 @@ static __always_inline int trace_get_context_bit(void)
> # define trace_warn_on_no_rcu(ip) false
> #endif
>
> -/*
> - * Preemption is promised to be disabled when return bit >= 0.
> - */
> static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsigned long pip,
> int start)
> {
> @@ -182,18 +179,11 @@ static __always_inline int trace_test_and_set_recursion(unsigned long ip, unsign
> val |= 1 << bit;
> current->trace_recursion = val;
> barrier();
> -
> - preempt_disable_notrace();
> -
> return bit;
> }
>
> -/*
> - * Preemption will be enabled (if it was previously enabled).
> - */
> static __always_inline void trace_clear_recursion(int bit)
> {
> - preempt_enable_notrace();
> barrier();
> trace_recursion_clear(bit);
> }
> @@ -205,12 +195,18 @@ static __always_inline void trace_clear_recursion(int bit)
> * tracing recursed in the same context (normal vs interrupt),
> *
> * Returns: -1 if a recursion happened.
> - * >= 0 if no recursion.
> + * >= 0 if no recursion and preemption will be disabled.
> */
> static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
> unsigned long parent_ip)
> {
> - return trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START);
> + int bit;
> +
> + bit = trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START);
> + if (unlikely(bit < 0))
> + return bit;
> + preempt_disable_notrace();
> + return bit;
> }
>
> /**
> @@ -221,6 +217,33 @@ static __always_inline int ftrace_test_recursion_trylock(unsigned long ip,
> */
> static __always_inline void ftrace_test_recursion_unlock(int bit)
> {
> + preempt_enable_notrace();
> + trace_clear_recursion(bit);
> +}
> +
> +/**
> + * test_recursion_try_acquire - tests for recursion in same context
> + *
> + * This will detect recursion of a function.
> + *
> + * Returns: -1 if a recursion happened.
> + * >= 0 if no recursion
> + */
> +static __always_inline int test_recursion_try_acquire(unsigned long ip,
> + unsigned long parent_ip)
> +{
> + return trace_test_and_set_recursion(ip, parent_ip, TRACE_FTRACE_START);
> +}
> +
> +/**
> + * test_recursion_release - called after a success of test_recursion_try_acquire()
> + * @bit: The return of a successful test_recursion_try_acquire()
> + *
> + * This releases the recursion lock taken by a non-negative return call
> + * by test_recursion_try_acquire().
> + */
> +static __always_inline void test_recursion_release(int bit)
> +{
> trace_clear_recursion(bit);
> }
>
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index c67bcc8..8ad3ab4 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -7647,6 +7647,7 @@ void ftrace_reset_array_ops(struct trace_array *tr)
> if (bit < 0)
> return;
>
> + preempt_disable();
> do_for_each_ftrace_op(op, ftrace_ops_list) {
> /* Stub functions don't need to be called nor tested */
> if (op->flags & FTRACE_OPS_FL_STUB)
> @@ -7668,6 +7669,7 @@ void ftrace_reset_array_ops(struct trace_array *tr)
> }
> } while_for_each_ftrace_op(op);
> out:
> + preempt_enable();
> trace_clear_recursion(bit);
> }
>
> --
> 1.8.3.1
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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