On Thu, 3 Oct 2024 11:16:35 -0400 Mathieu Desnoyers <[email protected]> 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 <[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]> > --- > 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" >
