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Date: Sat, 26 Jun 2021 14:42:49 -0400 (EDT)
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Robert Richter <rric@...nel.org>,
Gabriel Krisman Bertazi <krisman@...labora.com>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
netdev <netdev@...r.kernel.org>, bpf@...r.kernel.org
Subject: Re: [PATCH] tracepoint: Do not warn on EEXIST or ENOENT
----- Steven Rostedt <rostedt@...dmis.org> wrote:
> On Sat, 26 Jun 2021 11:41:57 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
>
> > If BPF is expected to register the same tracepoint with the same
> > callback and data more than once, then let's add a call to do that
> > without warning. Like I said, other callers expect the call to succeed
> > unless it's out of memory, which tends to cause other problems.
>
> If BPF is OK with registering the same probe more than once if user
> space expects it, we can add this patch, which allows the caller (in
> this case BPF) to not warn if the probe being registered is already
> registered, and keeps the idea that a probe registered twice is a bug
> for all other use cases.
How can removal of the duplicates be non buggy then ? The first removal will match both probes.
Thanks,
Mathieu
>
> -- Steve
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 13f65420f188..656d22cf42fc 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -36,10 +36,11 @@ struct trace_eval_map {
> extern struct srcu_struct tracepoint_srcu;
>
> extern int
> -tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data);
> +tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data,
> + bool no_warn);
> extern int
> tracepoint_probe_register_prio(struct tracepoint *tp, void *probe, void *data,
> - int prio);
> + int prio, bool no_warn);
> extern int
> tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data);
> extern void
> @@ -250,14 +251,16 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> register_trace_##name(void (*probe)(data_proto), void *data) \
> { \
> return tracepoint_probe_register(&__tracepoint_##name, \
> - (void *)probe, data); \
> + (void *)probe, data, \
> + false); \
> } \
> static inline int \
> register_trace_prio_##name(void (*probe)(data_proto), void *data,\
> int prio) \
> { \
> return tracepoint_probe_register_prio(&__tracepoint_##name, \
> - (void *)probe, data, prio); \
> + (void *)probe, data, \
> + prio, false); \
> } \
> static inline int \
> unregister_trace_##name(void (*probe)(data_proto), void *data) \
> diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
> index 8bcffbdef3d3..b76738e61eee 100644
> --- a/kernel/kcsan/kcsan_test.c
> +++ b/kernel/kcsan/kcsan_test.c
> @@ -1160,7 +1160,7 @@ static void register_tracepoints(struct tracepoint *tp, void *ignore)
> {
> check_trace_callback_type_console(probe_console);
> if (!strcmp(tp->name, "console"))
> - WARN_ON(tracepoint_probe_register(tp, probe_console, NULL));
> + WARN_ON(tracepoint_probe_register(tp, probe_console, NULL, false));
> }
>
> __no_kcsan
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 7a52bc172841..3d3a80db40b5 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1840,7 +1840,7 @@ static int __bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *
> if (prog->aux->max_tp_access > btp->writable_size)
> return -EINVAL;
>
> - return tracepoint_probe_register(tp, (void *)btp->bpf_func, prog);
> + return tracepoint_probe_register(tp, (void *)btp->bpf_func, prog, true);
> }
>
> int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *prog)
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 80e96989770e..07986569b1b9 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -500,7 +500,7 @@ int trace_event_reg(struct trace_event_call *call,
> case TRACE_REG_REGISTER:
> return tracepoint_probe_register(call->tp,
> call->class->probe,
> - file);
> + file, false);
> case TRACE_REG_UNREGISTER:
> tracepoint_probe_unregister(call->tp,
> call->class->probe,
> @@ -511,7 +511,7 @@ int trace_event_reg(struct trace_event_call *call,
> case TRACE_REG_PERF_REGISTER:
> return tracepoint_probe_register(call->tp,
> call->class->perf_probe,
> - call);
> + call, false);
> case TRACE_REG_PERF_UNREGISTER:
> tracepoint_probe_unregister(call->tp,
> call->class->perf_probe,
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 9f478d29b926..3c3a517b229e 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -273,7 +273,8 @@ static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func
> * Add the probe function to a tracepoint.
> */
> static int tracepoint_add_func(struct tracepoint *tp,
> - struct tracepoint_func *func, int prio)
> + struct tracepoint_func *func, int prio,
> + bool no_warn)
> {
> struct tracepoint_func *old, *tp_funcs;
> int ret;
> @@ -288,7 +289,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
> lockdep_is_held(&tracepoints_mutex));
> old = func_add(&tp_funcs, func, prio);
> if (IS_ERR(old)) {
> - WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
> + WARN_ON_ONCE(!no_warn && PTR_ERR(old) != -ENOMEM);
> return PTR_ERR(old);
> }
>
> @@ -349,6 +350,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
> * @probe: probe handler
> * @data: tracepoint data
> * @prio: priority of this function over other registered functions
> + * @no_warn: Do not warn if the tracepoint is already registered
> *
> * Returns 0 if ok, error value on error.
> * Note: if @tp is within a module, the caller is responsible for
> @@ -357,7 +359,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
> * within module exit functions.
> */
> int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
> - void *data, int prio)
> + void *data, int prio, bool no_warn)
> {
> struct tracepoint_func tp_func;
> int ret;
> @@ -366,7 +368,7 @@ int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
> tp_func.func = probe;
> tp_func.data = data;
> tp_func.prio = prio;
> - ret = tracepoint_add_func(tp, &tp_func, prio);
> + ret = tracepoint_add_func(tp, &tp_func, prio, no_warn);
> mutex_unlock(&tracepoints_mutex);
> return ret;
> }
> @@ -377,6 +379,7 @@ EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);
> * @tp: tracepoint
> * @probe: probe handler
> * @data: tracepoint data
> + * @no_warn: Do not warn if the tracepoint is already registered
> *
> * Returns 0 if ok, error value on error.
> * Note: if @tp is within a module, the caller is responsible for
> @@ -384,9 +387,11 @@ EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);
> * performed either with a tracepoint module going notifier, or from
> * within module exit functions.
> */
> -int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)
> +int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data,
> + bool no_warn)
> {
> - return tracepoint_probe_register_prio(tp, probe, data, TRACEPOINT_DEFAULT_PRIO);
> + return tracepoint_probe_register_prio(tp, probe, data,
> + TRACEPOINT_DEFAULT_PRIO, no_warn);
> }
> EXPORT_SYMBOL_GPL(tracepoint_probe_register);
>
> diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
> index 4acf4251ee04..a9331c967690 100644
> --- a/mm/kfence/kfence_test.c
> +++ b/mm/kfence/kfence_test.c
> @@ -820,7 +820,7 @@ static void register_tracepoints(struct tracepoint *tp, void *ignore)
> {
> check_trace_callback_type_console(probe_console);
> if (!strcmp(tp->name, "console"))
> - WARN_ON(tracepoint_probe_register(tp, probe_console, NULL));
> + WARN_ON(tracepoint_probe_register(tp, probe_console, NULL, true));
> }
>
> static void unregister_tracepoints(struct tracepoint *tp, void *ignore)
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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