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 <[email protected]> Cc: Michael Jeanson <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Masami Hiramatsu <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Alexei Starovoitov <[email protected]> Cc: Yonghong Song <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Mark Rutland <[email protected]> Cc: Alexander Shishkin <[email protected]> Cc: Namhyung Kim <[email protected]> Cc: Andrii Nakryiko <[email protected]> Cc: [email protected] Cc: Joel Fernandes <[email protected]> --- Changes since v3: - Add comment above __DO_TRACE() which describes the preempt off vs Tasks Trace RCU for syscall=0 vs syscall=1. --- include/linux/tracepoint.h | 18 ++++++++++++++++-- init/Kconfig | 1 + 2 files changed, 17 insertions(+), 2 deletions(-) diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 76e441b39a96..0dc67fad706c 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 @@ -196,6 +198,12 @@ 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. + * + * With @syscall=0, the tracepoint callback array dereference is + * protected by disabling preemption. + * With @syscall=1, the tracepoint callback array dereference is + * protected by Tasks Trace RCU, which allows probes to handle page + * faults. */ #define __DO_TRACE(name, args, cond, syscall) \ do { \ @@ -204,11 +212,17 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) if (!(cond)) \ return; \ \ - preempt_disable_notrace(); \ + 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 530a382ee0fe..4ac3d1b48278 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1985,6 +1985,7 @@ config BINDGEN_VERSION_TEXT # config TRACEPOINTS bool + select TASKS_TRACE_RCU source "kernel/Kconfig.kexec" -- 2.39.2
