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Date: Wed, 9 Nov 2022 00:33:37 -0300
From: Rafael Mendonca <rafaelmendsr@...il.com>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
LKML <linux-kernel@...r.kernel.org>,
Tzvetomir Stoyanov <tz.stoyanov@...il.com>,
Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 2/3] tracing/eprobe: Add eprobe filter support
On Mon, Aug 01, 2022 at 11:32:25AM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>
> Add the filter option to the event probe. This is useful if user wants
> to derive a new event based on the condition of the original event.
>
> E.g.
> echo 'e:egroup/stat_runtime_4core sched/sched_stat_runtime \
> runtime=$runtime:u32 if cpu < 4' >> ../dynamic_events
>
> Then it can filter the events only on first 4 cores.
> Note that the fields used for 'if' must be the fields in the original
> events, not eprobe events.
>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
> kernel/trace/trace_eprobe.c | 104 ++++++++++++++++++++++++++++++++++++++++---
> kernel/trace/trace_probe.h | 3 +
> 2 files changed, 98 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
> index 4a0e9d927443..8b32d1a3b9c7 100644
> --- a/kernel/trace/trace_eprobe.c
> +++ b/kernel/trace/trace_eprobe.c
> @@ -26,6 +26,9 @@ struct trace_eprobe {
> /* tracepoint event */
> const char *event_name;
>
> + /* filter string for the tracepoint */
> + char *filter_str;
> +
> struct trace_event_call *event;
>
> struct dyn_event devent;
> @@ -589,14 +592,15 @@ static struct event_trigger_data *
> new_eprobe_trigger(struct trace_eprobe *ep, struct trace_event_file *file)
> {
> struct event_trigger_data *trigger;
> + struct event_filter *filter = NULL;
> struct eprobe_data *edata;
> + int ret;
>
> edata = kzalloc(sizeof(*edata), GFP_KERNEL);
> trigger = kzalloc(sizeof(*trigger), GFP_KERNEL);
> if (!trigger || !edata) {
> - kfree(edata);
> - kfree(trigger);
> - return ERR_PTR(-ENOMEM);
> + ret = -ENOMEM;
> + goto error;
> }
>
> trigger->flags = EVENT_TRIGGER_FL_PROBE;
> @@ -611,13 +615,25 @@ new_eprobe_trigger(struct trace_eprobe *ep, struct trace_event_file *file)
> trigger->cmd_ops = &event_trigger_cmd;
>
> INIT_LIST_HEAD(&trigger->list);
> - RCU_INIT_POINTER(trigger->filter, NULL);
> +
> + if (ep->filter_str) {
> + ret = create_event_filter(file->tr, file->event_call,
Hi Masami,
I was playing around with the filter option and couldn't get it to work the way
I was expecting. For example, I'm getting the following output:
root@...alhost:/sys/kernel/tracing# echo 'e syscalls/sys_enter_openat \
flags_rename=$flags:u32 if flags < 1000' >> dynamic_events
root@...alhost:/sys/kernel/tracing# echo 1 > events/eprobes/sys_enter_openat/enable
[ 114.551550] event trace: Could not enable event sys_enter_openat
-bash: echo: write error: Invalid argument
I was wondering if the trace_event_call passed to create_event_filter()
shouldn't be 'ep->event' instead of 'file->event_call' as such:
diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index e888446d80fa..123d2c0a6b68 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -643,7 +643,7 @@ new_eprobe_trigger(struct trace_eprobe *ep, struct
trace_event_file *file)
INIT_LIST_HEAD(&trigger->list);
if (ep->filter_str) {
- ret = create_event_filter(file->tr, file->event_call,
+ ret = create_event_filter(file->tr, ep->event,
ep->filter_str, false, &filter);
if (ret)
goto error;
Applying the above change seems to make it work the way I was expecting:
root@...alhost:/sys/kernel/tracing# echo 'e syscalls/sys_enter_openat \
flags_rename=$flags:u32 if flags < 1000' >> dynamic_events
root@...alhost:/sys/kernel/tracing# echo 1 > events/eprobes/sys_enter_openat/enable
root@...alhost:/sys/kernel/tracing# tail trace
cat-241 [000] ...1. 266.498449: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
cat-242 [000] ...1. 266.977640: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
cat-242 [000] ...1. 266.979883: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
bash-223 [000] ...1. 272.322714: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=577
cat-243 [000] ...1. 273.630900: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
cat-243 [000] ...1. 273.633464: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
tail-244 [000] ...1. 300.013530: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
tail-244 [000] ...1. 300.018584: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
tail-245 [000] ...1. 301.237883: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
tail-245 [000] ...1. 301.243375: sys_enter_openat: (syscalls.sys_enter_openat) flags_rename=0
I'm not familiar with the eprobe code, sorry if this is nonsense.
> + ep->filter_str, false, &filter);
> + if (ret)
> + goto error;
> + }
> + RCU_INIT_POINTER(trigger->filter, filter);
>
> edata->file = file;
> edata->ep = ep;
> trigger->private_data = edata;
>
> return trigger;
> +error:
> + free_event_filter(filter);
> + kfree(edata);
> + kfree(trigger);
> + return ERR_PTR(ret);
> }
>
> static int enable_eprobe(struct trace_eprobe *ep,
> @@ -651,6 +667,7 @@ static int disable_eprobe(struct trace_eprobe *ep,
> {
> struct event_trigger_data *trigger = NULL, *iter;
> struct trace_event_file *file;
> + struct event_filter *filter;
> struct eprobe_data *edata;
>
> file = find_event_file(tr, ep->event_system, ep->event_name);
> @@ -677,6 +694,10 @@ static int disable_eprobe(struct trace_eprobe *ep,
> /* Make sure nothing is using the edata or trigger */
> tracepoint_synchronize_unregister();
>
> + filter = rcu_access_pointer(trigger->filter);
> +
> + if (filter)
> + free_event_filter(filter);
> kfree(edata);
> kfree(trigger);
>
> @@ -848,12 +869,62 @@ static int trace_eprobe_tp_update_arg(struct trace_eprobe *ep, const char *argv[
> return ret;
> }
>
> +static int trace_eprobe_parse_filter(struct trace_eprobe *ep, int argc, const char *argv[])
> +{
> + struct event_filter *dummy;
> + int i, ret, len = 0;
> + char *p;
> +
> + if (argc == 0) {
> + trace_probe_log_err(0, NO_EP_FILTER);
> + return -EINVAL;
> + }
> +
> + /* Recover the filter string */
> + for (i = 0; i < argc; i++)
> + len += strlen(argv[i]) + 1;
> +
> + ep->filter_str = kzalloc(len, GFP_KERNEL);
> + if (!ep->filter_str)
> + return -ENOMEM;
> +
> + p = ep->filter_str;
> + for (i = 0; i < argc; i++) {
> + ret = snprintf(p, len, "%s ", argv[i]);
> + if (ret < 0)
> + goto error;
> + if (ret > len) {
> + ret = -E2BIG;
> + goto error;
> + }
> + p += ret;
> + len -= ret;
> + }
> + p[-1] = '\0';
> +
> + /*
> + * Ensure the filter string can be parsed correctly. Note, this
> + * filter string is for the original event, not for the eprobe.
> + */
> + ret = create_event_filter(top_trace_array(), ep->event, ep->filter_str,
> + true, &dummy);
> + free_event_filter(dummy);
> + if (ret)
> + goto error;
> +
> + return 0;
> +error:
> + kfree(ep->filter_str);
> + ep->filter_str = NULL;
> + return ret;
> +}
> +
> static int __trace_eprobe_create(int argc, const char *argv[])
> {
> /*
> * Argument syntax:
> - * e[:[GRP/][ENAME]] SYSTEM.EVENT [FETCHARGS]
> - * Fetch args:
> + * e[:[GRP/][ENAME]] SYSTEM.EVENT [FETCHARGS] [if FILTER]
> + * Fetch args (no space):
> * <name>=$<field>[:TYPE]
> */
> const char *event = NULL, *group = EPROBE_EVENT_SYSTEM;
> @@ -863,8 +934,8 @@ static int __trace_eprobe_create(int argc, const char *argv[])
> char buf1[MAX_EVENT_NAME_LEN];
> char buf2[MAX_EVENT_NAME_LEN];
> char gbuf[MAX_EVENT_NAME_LEN];
> - int ret = 0;
> - int i;
> + int ret = 0, filter_idx = 0;
> + int i, filter_cnt;
>
> if (argc < 2 || argv[0][0] != 'e')
> return -ECANCELED;
> @@ -894,6 +965,15 @@ static int __trace_eprobe_create(int argc, const char *argv[])
> event = buf1;
> }
>
> + for (i = 2; i < argc; i++) {
> + if (!strcmp(argv[i], "if")) {
> + filter_idx = i + 1;
> + filter_cnt = argc - filter_idx;
> + argc = i;
> + break;
> + }
> + }
> +
> mutex_lock(&event_mutex);
> event_call = find_and_get_event(sys_name, sys_event);
> ep = alloc_event_probe(group, event, event_call, argc - 2);
> @@ -909,6 +989,14 @@ static int __trace_eprobe_create(int argc, const char *argv[])
> goto error;
> }
>
> + if (filter_idx) {
> + trace_probe_log_set_index(filter_idx);
> + ret = trace_eprobe_parse_filter(ep, filter_cnt, argv + filter_idx);
> + if (ret)
> + goto parse_error;
> + } else
> + ep->filter_str = NULL;
> +
> argc -= 2; argv += 2;
> /* parse arguments */
> for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
> index 3b3869ae8cfd..de38f1c03776 100644
> --- a/kernel/trace/trace_probe.h
> +++ b/kernel/trace/trace_probe.h
> @@ -445,7 +445,8 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
> C(SAME_PROBE, "There is already the exact same probe event"),\
> C(NO_EVENT_INFO, "This requires both group and event name to attach"),\
> C(BAD_ATTACH_EVENT, "Attached event does not exist"),\
> - C(BAD_ATTACH_ARG, "Attached event does not have this field"),
> + C(BAD_ATTACH_ARG, "Attached event does not have this field"),\
> + C(NO_EP_FILTER, "No filter rule after 'if'"),
>
> #undef C
> #define C(a, b) TP_ERR_##a
>
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