On Thu, 3 Oct 2024 11:16:35 -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 | 25 +++++++++++++++++--------
> init/Kconfig | 1 +
> 2 files changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 666499b9f3be..6faf34e5efc9 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>
>
> @@ -109,6 +110,7 @@ void for_each_tracepoint_in_module(struct module *mod,
> #ifdef CONFIG_TRACEPOINTS
> static inline void tracepoint_synchronize_unregister(void)
> {
> + synchronize_rcu_tasks_trace();
> synchronize_srcu(&tracepoint_srcu);
> synchronize_rcu();
> }
> @@ -211,7 +213,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> * it_func[0] is never NULL because there is at least one element in the array
> * when the array itself is non NULL.
> */
> -#define __DO_TRACE(name, args, cond, rcuidle) \
> +#define __DO_TRACE(name, args, cond, rcuidle, syscall) \
> do { \
> int __maybe_unused __idx = 0; \
> \
> @@ -222,8 +224,12 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> "Bad RCU usage for tracepoint")) \
> return; \
> \
> - /* keep srcu and sched-rcu usage consistent */ \
> - preempt_disable_notrace(); \
> + if (syscall) { \
> + rcu_read_lock_trace(); \
> + } else { \
> + /* keep srcu and sched-rcu usage consistent */ \
> + preempt_disable_notrace(); \
> + } \
> \
I'm thinking we just use rcu_read_lock_trace() and get rid of the
preempt_disable and srcu locks for all tracepoints. Oh crap! I should get
rid of srcu locking too, as it was only needed for the rcuidle code :-p
-- Steve
> /* \
> * For rcuidle callers, use srcu since sched-rcu \
> @@ -241,7 +247,10 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> srcu_read_unlock_notrace(&tracepoint_srcu, __idx);\
> } \
> \
> - preempt_enable_notrace(); \
> + if (syscall) \
> + rcu_read_unlock_trace(); \
> + else \
> + preempt_enable_notrace(); \
> } while (0)
>
> #ifndef MODULE
> @@ -251,7 +260,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> if (static_key_false(&__tracepoint_##name.key)) \
> __DO_TRACE(name, \
> TP_ARGS(args), \
> - TP_CONDITION(cond), 1); \
> + TP_CONDITION(cond), 1, 0); \
> }
> #else
> #define __DECLARE_TRACE_RCU(name, proto, args, cond)
> @@ -284,7 +293,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> if (static_key_false(&__tracepoint_##name.key)) \
> __DO_TRACE(name, \
> TP_ARGS(args), \
> - TP_CONDITION(cond), 0); \
> + TP_CONDITION(cond), 0, 0); \
> if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
> WARN_ONCE(!rcu_is_watching(), \
> "RCU not watching for tracepoint"); \
> @@ -295,7 +304,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> if (static_key_false(&__tracepoint_##name.key)) \
> __DO_TRACE(name, \
> TP_ARGS(args), \
> - TP_CONDITION(cond), 1); \
> + TP_CONDITION(cond), 1, 0); \
> } \
> static inline int \
> register_trace_##name(void (*probe)(data_proto), void *data) \
> @@ -330,7 +339,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> if (static_key_false(&__tracepoint_##name.key)) \
> __DO_TRACE(name, \
> TP_ARGS(args), \
> - TP_CONDITION(cond), 0); \
> + TP_CONDITION(cond), 0, 1); \
> if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
> WARN_ONCE(!rcu_is_watching(), \
> "RCU not watching for tracepoint"); \
> 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"
>
