diff mbox series

[v1,3/8] tracing/perf: guard syscall probe with preempt_notrace

Message ID 20241003151638.1608537-4-mathieu.desnoyers@efficios.com (mailing list archive)
State Superseded
Headers show
Series tracing: Allow system call tracepoints to handle page faults | expand

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Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Mathieu Desnoyers Oct. 3, 2024, 3:16 p.m. UTC 
In preparation for allowing system call enter/exit instrumentation to
handle page faults, make sure that perf can handle this change by
explicitly disabling preemption within the perf system call tracepoint
probes to respect the current expectations within perf ring buffer code.

This change does not yet allow perf to take page faults per se within
its probe, but allows its existing probes to adapt to the upcoming
change.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michael Jeanson <mjeanson@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf@vger.kernel.org
Cc: Joel Fernandes <joel@joelfernandes.org>
---
 include/trace/perf.h          | 41 +++++++++++++++++++++++++++++++----
 kernel/trace/trace_syscalls.c | 12 ++++++++++
 2 files changed, 49 insertions(+), 4 deletions(-)

Comments

Steven Rostedt Oct. 3, 2024, 10:25 p.m. UTC | #1 
On Thu,  3 Oct 2024 11:16:33 -0400
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> In preparation for allowing system call enter/exit instrumentation to
> handle page faults, make sure that perf can handle this change by
> explicitly disabling preemption within the perf system call tracepoint
> probes to respect the current expectations within perf ring buffer code.
> 
> This change does not yet allow perf to take page faults per se within
> its probe, but allows its existing probes to adapt to the upcoming
> change.

Frederic,

Does the perf ring buffer expect preemption to be disabled when used?

In other words, is this patch needed?

-- Steve


> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Michael Jeanson <mjeanson@efficios.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Yonghong Song <yhs@fb.com>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Cc: bpf@vger.kernel.org
> Cc: Joel Fernandes <joel@joelfernandes.org>
> ---
>  include/trace/perf.h          | 41 +++++++++++++++++++++++++++++++----
>  kernel/trace/trace_syscalls.c | 12 ++++++++++
>  2 files changed, 49 insertions(+), 4 deletions(-)
> 
> diff --git a/include/trace/perf.h b/include/trace/perf.h
> index ded997af481e..5650c1bad088 100644
> --- a/include/trace/perf.h
> +++ b/include/trace/perf.h
> @@ -12,10 +12,10 @@
>  #undef __perf_task
>  #define __perf_task(t)	(__task = (t))
>  
> -#undef DECLARE_EVENT_CLASS
> -#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
> +#undef __DECLARE_EVENT_CLASS
> +#define __DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
>  static notrace void							\
> -perf_trace_##call(void *__data, proto)					\
> +do_perf_trace_##call(void *__data, proto)				\
>  {									\
>  	struct trace_event_call *event_call = __data;			\
>  	struct trace_event_data_offsets_##call __maybe_unused __data_offsets;\
> @@ -55,8 +55,38 @@ perf_trace_##call(void *__data, proto)					\
>  				  head, __task);			\
>  }
>  
> +/*
> + * Define unused __count and __task variables to use @args to pass
> + * arguments to do_perf_trace_##call. This is needed because the
> + * macros __perf_count and __perf_task introduce the side-effect to
> + * store copies into those local variables.
> + */
> +#undef DECLARE_EVENT_CLASS
> +#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
> +__DECLARE_EVENT_CLASS(call, PARAMS(proto), PARAMS(args), PARAMS(tstruct), \
> +		      PARAMS(assign), PARAMS(print))			\
> +static notrace void							\
> +perf_trace_##call(void *__data, proto)					\
> +{									\
> +	u64 __count __attribute__((unused));				\
> +	struct task_struct *__task __attribute__((unused));		\
> +									\
> +	do_perf_trace_##call(__data, args);				\
> +}
> +
>  #undef DECLARE_EVENT_SYSCALL_CLASS
> -#define DECLARE_EVENT_SYSCALL_CLASS DECLARE_EVENT_CLASS
> +#define DECLARE_EVENT_SYSCALL_CLASS(call, proto, args, tstruct, assign, print) \
> +__DECLARE_EVENT_CLASS(call, PARAMS(proto), PARAMS(args), PARAMS(tstruct), \
> +		      PARAMS(assign), PARAMS(print))			\
> +static notrace void							\
> +perf_trace_##call(void *__data, proto)					\
> +{									\
> +	u64 __count __attribute__((unused));				\
> +	struct task_struct *__task __attribute__((unused));		\
> +									\
> +	guard(preempt_notrace)();					\
> +	do_perf_trace_##call(__data, args);				\
> +}
>  
>  /*
>   * This part is compiled out, it is only here as a build time check
> @@ -76,4 +106,7 @@ static inline void perf_test_probe_##call(void)				\
>  	DEFINE_EVENT(template, name, PARAMS(proto), PARAMS(args))
>  
>  #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
> +
> +#undef __DECLARE_EVENT_CLASS
> +
>  #endif /* CONFIG_PERF_EVENTS */
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index ab4db8c23f36..edcfa47446c7 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -596,6 +596,12 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
>  	int rctx;
>  	int size;
>  
> +	/*
> +	 * Syscall probe called with preemption enabled, but the ring
> +	 * buffer and per-cpu data require preemption to be disabled.
> +	 */
> +	guard(preempt_notrace)();
> +
>  	syscall_nr = trace_get_syscall_nr(current, regs);
>  	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
>  		return;
> @@ -698,6 +704,12 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
>  	int rctx;
>  	int size;
>  
> +	/*
> +	 * Syscall probe called with preemption enabled, but the ring
> +	 * buffer and per-cpu data require preemption to be disabled.
> +	 */
> +	guard(preempt_notrace)();
> +
>  	syscall_nr = trace_get_syscall_nr(current, regs);
>  	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
>  		return;
Frederic Weisbecker Oct. 4, 2024, 12:17 a.m. UTC | #2 
Le Thu, Oct 03, 2024 at 06:25:08PM -0400, Steven Rostedt a écrit :
> On Thu,  3 Oct 2024 11:16:33 -0400
> Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> 
> > In preparation for allowing system call enter/exit instrumentation to
> > handle page faults, make sure that perf can handle this change by
> > explicitly disabling preemption within the perf system call tracepoint
> > probes to respect the current expectations within perf ring buffer code.
> > 
> > This change does not yet allow perf to take page faults per se within
> > its probe, but allows its existing probes to adapt to the upcoming
> > change.
> 
> Frederic,
> 
> Does the perf ring buffer expect preemption to be disabled when used?
> 
> In other words, is this patch needed?

At least the trace events perf callback requires that because it uses
a per cpu buffer (see perf_trace_buf_alloc()).

Thanks.
diff mbox series

Patch

diff --git a/include/trace/perf.h b/include/trace/perf.h
index ded997af481e..5650c1bad088 100644
--- a/include/trace/perf.h
+++ b/include/trace/perf.h
@@ -12,10 +12,10 @@ 
 #undef __perf_task
 #define __perf_task(t)	(__task = (t))
 
-#undef DECLARE_EVENT_CLASS
-#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
+#undef __DECLARE_EVENT_CLASS
+#define __DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
 static notrace void							\
-perf_trace_##call(void *__data, proto)					\
+do_perf_trace_##call(void *__data, proto)				\
 {									\
 	struct trace_event_call *event_call = __data;			\
 	struct trace_event_data_offsets_##call __maybe_unused __data_offsets;\
@@ -55,8 +55,38 @@  perf_trace_##call(void *__data, proto)					\
 				  head, __task);			\
 }
 
+/*
+ * Define unused __count and __task variables to use @args to pass
+ * arguments to do_perf_trace_##call. This is needed because the
+ * macros __perf_count and __perf_task introduce the side-effect to
+ * store copies into those local variables.
+ */
+#undef DECLARE_EVENT_CLASS
+#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print)	\
+__DECLARE_EVENT_CLASS(call, PARAMS(proto), PARAMS(args), PARAMS(tstruct), \
+		      PARAMS(assign), PARAMS(print))			\
+static notrace void							\
+perf_trace_##call(void *__data, proto)					\
+{									\
+	u64 __count __attribute__((unused));				\
+	struct task_struct *__task __attribute__((unused));		\
+									\
+	do_perf_trace_##call(__data, args);				\
+}
+
 #undef DECLARE_EVENT_SYSCALL_CLASS
-#define DECLARE_EVENT_SYSCALL_CLASS DECLARE_EVENT_CLASS
+#define DECLARE_EVENT_SYSCALL_CLASS(call, proto, args, tstruct, assign, print) \
+__DECLARE_EVENT_CLASS(call, PARAMS(proto), PARAMS(args), PARAMS(tstruct), \
+		      PARAMS(assign), PARAMS(print))			\
+static notrace void							\
+perf_trace_##call(void *__data, proto)					\
+{									\
+	u64 __count __attribute__((unused));				\
+	struct task_struct *__task __attribute__((unused));		\
+									\
+	guard(preempt_notrace)();					\
+	do_perf_trace_##call(__data, args);				\
+}
 
 /*
  * This part is compiled out, it is only here as a build time check
@@ -76,4 +106,7 @@  static inline void perf_test_probe_##call(void)				\
 	DEFINE_EVENT(template, name, PARAMS(proto), PARAMS(args))
 
 #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
+
+#undef __DECLARE_EVENT_CLASS
+
 #endif /* CONFIG_PERF_EVENTS */
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index ab4db8c23f36..edcfa47446c7 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -596,6 +596,12 @@  static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	int rctx;
 	int size;
 
+	/*
+	 * Syscall probe called with preemption enabled, but the ring
+	 * buffer and per-cpu data require preemption to be disabled.
+	 */
+	guard(preempt_notrace)();
+
 	syscall_nr = trace_get_syscall_nr(current, regs);
 	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
 		return;
@@ -698,6 +704,12 @@  static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 	int rctx;
 	int size;
 
+	/*
+	 * Syscall probe called with preemption enabled, but the ring
+	 * buffer and per-cpu data require preemption to be disabled.
+	 */
+	guard(preempt_notrace)();
+
 	syscall_nr = trace_get_syscall_nr(current, regs);
 	if (syscall_nr < 0 || syscall_nr >= NR_syscalls)
 		return;