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Message-Id: <20241027231930.941d6c1f21e2b4668af44df8@kernel.org>
Date: Sun, 27 Oct 2024 23:19:30 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
linux-kernel@...r.kernel.org, Michael Jeanson <mjeanson@...icios.com>,
Masami Hiramatsu <mhiramat@...nel.org>, Peter Zijlstra
<peterz@...radead.org>, Alexei Starovoitov <ast@...nel.org>, Yonghong Song
<yhs@...com>, "Paul E . McKenney" <paulmck@...nel.org>, Ingo Molnar
<mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark
Rutland <mark.rutland@....com>, Alexander Shishkin
<alexander.shishkin@...ux.intel.com>, Namhyung Kim <namhyung@...nel.org>,
Andrii Nakryiko <andrii.nakryiko@...il.com>, bpf@...r.kernel.org, Joel
Fernandes <joel@...lfernandes.org>, Jordan Rife <jrife@...gle.com>
Subject: Re: [RFC PATCH v3 2/3] tracing: Introduce tracepoint_is_syscall()
On Sat, 26 Oct 2024 20:08:40 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:
> On Sat, 26 Oct 2024 11:46:28 -0400
> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
>
> > Introduce a "syscall" flag within the extended structure to know whether
> > a tracepoint needs rcu tasks trace grace period before reclaim.
> > This can be queried using tracepoint_is_syscall().
> >
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Michael Jeanson <mjeanson@...icios.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Masami Hiramatsu <mhiramat@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > Cc: Yonghong Song <yhs@...com>
> > Cc: Paul E. McKenney <paulmck@...nel.org>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>
> > Cc: bpf@...r.kernel.org
> > Cc: Joel Fernandes <joel@...lfernandes.org>
> > Cc: Jordan Rife <jrife@...gle.com>
> > ---
> > include/linux/tracepoint-defs.h | 2 ++
> > include/linux/tracepoint.h | 24 ++++++++++++++++++++++++
> > include/trace/define_trace.h | 2 +-
> > 3 files changed, 27 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/tracepoint-defs.h b/include/linux/tracepoint-defs.h
> > index 967c08d9da84..53119e074c87 100644
> > --- a/include/linux/tracepoint-defs.h
> > +++ b/include/linux/tracepoint-defs.h
> > @@ -32,6 +32,8 @@ struct tracepoint_func {
> > struct tracepoint_ext {
> > int (*regfunc)(void);
> > void (*unregfunc)(void);
> > + /* Flags. */
> > + unsigned int syscall:1;
>
> I wonder if we should call it "sleepable" instead? For this patch set
> do we really care if it's a system call or not? It's really if the
> tracepoint is sleepable or not that's the issue. System calls are just
> one user of it, there may be more in the future, and the changes to BPF
> will still be needed.
I agree with this. Even if currently we restrict only syscall events
can be sleep, "tracepoint_is_syscall()" requires to add comment to
explain why on all call sites e.g.
/*
* The syscall event is only sleepable event, so we ensure it is
* syscall event for checking sleepable or not.
*/
If it called tracepoint_is_sleepable(), we don't need such comment.
Thank you,
>
> Other than that, I think this could work.
>
> -- Steve
>
>
> > };
> >
> > struct tracepoint {
> > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> > index 83dc24ee8b13..93e70bc64533 100644
> > --- a/include/linux/tracepoint.h
> > +++ b/include/linux/tracepoint.h
> > @@ -104,6 +104,12 @@ void for_each_tracepoint_in_module(struct module *mod,
> > * tracepoint_synchronize_unregister must be called between the last tracepoint
> > * probe unregistration and the end of module exit to make sure there is no
> > * caller executing a probe when it is freed.
> > + *
> > + * An alternative is to use the following for batch reclaim associated
> > + * with a given tracepoint:
> > + *
> > + * - tracepoint_is_syscall() == false: call_rcu()
> > + * - tracepoint_is_syscall() == true: call_rcu_tasks_trace()
> > */
> > #ifdef CONFIG_TRACEPOINTS
> > static inline void tracepoint_synchronize_unregister(void)
> > @@ -111,9 +117,17 @@ static inline void tracepoint_synchronize_unregister(void)
> > synchronize_rcu_tasks_trace();
> > synchronize_rcu();
> > }
> > +static inline bool tracepoint_is_syscall(struct tracepoint *tp)
> > +{
> > + return tp->ext && tp->ext->syscall;
> > +}
> > #else
> > static inline void tracepoint_synchronize_unregister(void)
> > { }
> > +static inline bool tracepoint_is_syscall(struct tracepoint *tp)
> > +{
> > + return false;
> > +}
> > #endif
> >
> > #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
> > @@ -345,6 +359,15 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> > struct tracepoint_ext __tracepoint_ext_##_name = { \
> > .regfunc = _reg, \
> > .unregfunc = _unreg, \
> > + .syscall = false, \
> > + }; \
> > + __DEFINE_TRACE_EXT(_name, &__tracepoint_ext_##_name, PARAMS(_proto), PARAMS(_args));
> > +
> > +#define DEFINE_TRACE_SYSCALL(_name, _reg, _unreg, _proto, _args) \
> > + struct tracepoint_ext __tracepoint_ext_##_name = { \
> > + .regfunc = _reg, \
> > + .unregfunc = _unreg, \
> > + .syscall = true, \
> > }; \
> > __DEFINE_TRACE_EXT(_name, &__tracepoint_ext_##_name, PARAMS(_proto), PARAMS(_args));
> >
> > @@ -389,6 +412,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> > #define __DECLARE_TRACE_SYSCALL __DECLARE_TRACE
> >
> > #define DEFINE_TRACE_FN(name, reg, unreg, proto, args)
> > +#define DEFINE_TRACE_SYSCALL(name, reg, unreg, proto, args)
> > #define DEFINE_TRACE(name, proto, args)
> > #define EXPORT_TRACEPOINT_SYMBOL_GPL(name)
> > #define EXPORT_TRACEPOINT_SYMBOL(name)
> > diff --git a/include/trace/define_trace.h b/include/trace/define_trace.h
> > index ff5fa17a6259..63fea2218afa 100644
> > --- a/include/trace/define_trace.h
> > +++ b/include/trace/define_trace.h
> > @@ -48,7 +48,7 @@
> >
> > #undef TRACE_EVENT_SYSCALL
> > #define TRACE_EVENT_SYSCALL(name, proto, args, struct, assign, print, reg, unreg) \
> > - DEFINE_TRACE_FN(name, reg, unreg, PARAMS(proto), PARAMS(args))
> > + DEFINE_TRACE_SYSCALL(name, reg, unreg, PARAMS(proto), PARAMS(args))
> >
> > #undef TRACE_EVENT_NOP
> > #define TRACE_EVENT_NOP(name, proto, args, struct, assign, print)
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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