On Fri, 4 Oct 2024 10:58:15 -0400
Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
> Use Tasks Trace RCU to protect iteration of system call enter/exit
> tracepoint probes to allow those probes to handle page faults.
>
> In preparation for this change, all tracers registering to system call
> enter/exit tracepoints should expect those to be called with preemption
> enabled.
>
> This allows tracers to fault-in userspace system call arguments such as
> path strings within their probe callbacks.
>
> 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/linux/tracepoint.h | 12 ++++++++++--
> init/Kconfig | 1 +
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 014790495ad8..cefd44b7c91f 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -17,6 +17,7 @@
> #include <linux/errno.h>
> #include <linux/types.h>
> #include <linux/rcupdate.h>
> +#include <linux/rcupdate_trace.h>
> #include <linux/tracepoint-defs.h>
> #include <linux/static_call.h>
>
> @@ -107,6 +108,7 @@ void for_each_tracepoint_in_module(struct module *mod,
> #ifdef CONFIG_TRACEPOINTS
> static inline void tracepoint_synchronize_unregister(void)
> {
> + synchronize_rcu_tasks_trace();
> synchronize_rcu();
> }
> #else
> @@ -204,11 +206,17 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> if (!(cond)) \
> return; \
> \
> - preempt_disable_notrace(); \
Should add a comment somewhere stating that the syscall version is to allow faults.
-- Steve
> + if (syscall) \
> + rcu_read_lock_trace(); \
> + else \
> + preempt_disable_notrace(); \
> \
> __DO_TRACE_CALL(name, TP_ARGS(args)); \
> \
> - preempt_enable_notrace(); \
> + if (syscall) \
> + rcu_read_unlock_trace(); \
> + else \
> + preempt_enable_notrace(); \
> } while (0)
>
> /*
> diff --git a/init/Kconfig b/init/Kconfig
> index fbd0cb06a50a..eedd0064fb36 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1984,6 +1984,7 @@ config BINDGEN_VERSION_TEXT
> #
> config TRACEPOINTS
> bool
> + select TASKS_TRACE_RCU
>
> source "kernel/Kconfig.kexec"
>
