| Message ID | 20241003151638.1608537-6-mathieu.desnoyers@efficios.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | tracing: Allow system call tracepoints to handle page faults | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Thu, 3 Oct 2024 11:16:35 -0400 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> 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@efficios.com> > Cc: Michael Jeanson <mjeanson@efficios.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Masami Hiramatsu <mhiramat@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Alexei Starovoitov <ast@kernel.org> > Cc: Yonghong Song <yhs@fb.com> > Cc: Paul E. McKenney <paulmck@kernel.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Arnaldo Carvalho de Melo <acme@kernel.org> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > Cc: Namhyung Kim <namhyung@kernel.org> > Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com> > Cc: bpf@vger.kernel.org > Cc: Joel Fernandes <joel@joelfernandes.org> > --- > 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" >
On 2024-10-04 00:29, Steven Rostedt wrote: > On Thu, 3 Oct 2024 11:16:35 -0400 [...[ >> -#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 How about we do it one step at a time ? First introduce use of the (lightly tested) rcu_read_lock_trace() (at least in comparison with preempt disable RCU) only for syscalls, and if this works well, then eventually consider moving the preempt off users to rcu_read_lock_trace as well ? Of course it should all work well, in theory. But considering the vast number of tracepoints we have in the kernel, I am reluctant to change too many things at once in that area. We may very well be bitten by unforeseen corner-cases. Thanks, Mathieu
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(); \ + } \ \ /* \ * 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"
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@efficios.com> Cc: Michael Jeanson <mjeanson@efficios.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Yonghong Song <yhs@fb.com> Cc: Paul E. McKenney <paulmck@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com> Cc: bpf@vger.kernel.org Cc: Joel Fernandes <joel@joelfernandes.org> --- include/linux/tracepoint.h | 25 +++++++++++++++++-------- init/Kconfig | 1 + 2 files changed, 18 insertions(+), 8 deletions(-)