On Mon, 9 Sep 2024 16:16:46 -0400
Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
> In preparation for allowing system call enter/exit instrumentation to
> handle page faults, make sure that ftrace can handle this change by
> explicitly disabling preemption within the ftrace system call tracepoint
> probes to respect the current expectations within ftrace ring buffer
> code.
>
> This change does not yet allow ftrace to take page faults per se within
> its probe, but allows its existing probes to adapt to the upcoming
> change.
OK, this looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Thank you,
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Michael Jeanson <mjeanson@xxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Yonghong Song <yhs@xxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
> Cc: bpf@xxxxxxxxxxxxxxx
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> ---
> include/trace/trace_events.h | 38 ++++++++++++++++++++++++++++-------
> kernel/trace/trace_syscalls.c | 12 +++++++++++
> 2 files changed, 43 insertions(+), 7 deletions(-)
>
> diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h
> index 8bcbb9ee44de..0228d9ed94a3 100644
> --- a/include/trace/trace_events.h
> +++ b/include/trace/trace_events.h
> @@ -263,6 +263,9 @@ static struct trace_event_fields trace_event_fields_##call[] = { \
> tstruct \
> {} };
>
> +#undef DECLARE_EVENT_SYSCALL_CLASS
> +#define DECLARE_EVENT_SYSCALL_CLASS DECLARE_EVENT_CLASS
> +
> #undef DEFINE_EVENT_PRINT
> #define DEFINE_EVENT_PRINT(template, name, proto, args, print)
>
> @@ -396,11 +399,11 @@ static inline notrace int trace_event_get_offsets_##call( \
>
> #include "stages/stage6_event_callback.h"
>
> -#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 \
> -trace_event_raw_event_##call(void *__data, proto) \
> +do_trace_event_raw_event_##call(void *__data, proto) \
> { \
> struct trace_event_file *trace_file = __data; \
> struct trace_event_data_offsets_##call __maybe_unused __data_offsets;\
> @@ -425,15 +428,34 @@ trace_event_raw_event_##call(void *__data, proto) \
> \
> trace_event_buffer_commit(&fbuffer); \
> }
> +
> +#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 \
> +trace_event_raw_event_##call(void *__data, proto) \
> +{ \
> + do_trace_event_raw_event_##call(__data, args); \
> +}
> +
> +#undef DECLARE_EVENT_SYSCALL_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 \
> +trace_event_raw_event_##call(void *__data, proto) \
> +{ \
> + guard(preempt_notrace)(); \
> + do_trace_event_raw_event_##call(__data, args); \
> +}
> +
> /*
> * The ftrace_test_probe is compiled out, it is only here as a build time check
> * to make sure that if the tracepoint handling changes, the ftrace probe will
> * fail to compile unless it too is updated.
> */
>
> -#undef DECLARE_EVENT_SYSCALL_CLASS
> -#define DECLARE_EVENT_SYSCALL_CLASS DECLARE_EVENT_CLASS
> -
> #undef DEFINE_EVENT
> #define DEFINE_EVENT(template, call, proto, args) \
> static inline void ftrace_test_probe_##call(void) \
> @@ -443,6 +465,8 @@ static inline void ftrace_test_probe_##call(void) \
>
> #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
>
> +#undef __DECLARE_EVENT_CLASS
> +
> #include "stages/stage7_class_define.h"
>
> #undef DECLARE_EVENT_CLASS
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index 067f8e2b930f..abf0e0b7cd0b 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -299,6 +299,12 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
> int syscall_nr;
> 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;
> @@ -338,6 +344,12 @@ static void ftrace_syscall_exit(void *data, struct pt_regs *regs, long ret)
> struct trace_event_buffer fbuffer;
> int syscall_nr;
>
> + /*
> + * 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;
> --
> 2.39.2
>
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
