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(); \
+ } \
\
/* \
* 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"
--
2.39.2On 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
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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