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Message-Id: <20221112142339.510c01a52ae8449e21f2d343@kernel.org>
Date: Sat, 12 Nov 2022 14:23:39 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Rafael Mendonca <rafaelmendsr@...il.com>
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 Wed, 9 Nov 2022 00:33:37 -0300
Rafael Mendonca <rafaelmendsr@...il.com> wrote:
> 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=$flags:u32 if flags < 1000' >> dynamic_events
> root@...alhost:/sys/kernel/tracing# echo 1 > events/eprobes/sys_enter_openat/enable
> [ 114.551550] event trace: Could not enable event sys_enter_openat
> -bash: echo: write error: Invalid argument
>
> I was wondering if the trace_event_call passed to create_event_filter()
> shouldn't be 'ep->event' instead of 'file->event_call' as such:
>
> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
> index e888446d80fa..123d2c0a6b68 100644
> --- a/kernel/trace/trace_eprobe.c
> +++ b/kernel/trace/trace_eprobe.c
> @@ -643,7 +643,7 @@ new_eprobe_trigger(struct trace_eprobe *ep, struct
> trace_event_file *file)
> INIT_LIST_HEAD(&trigger->list);
>
> if (ep->filter_str) {
> - ret = create_event_filter(file->tr, file->event_call,
> + ret = create_event_filter(file->tr, ep->event,
> ep->filter_str, false, &filter);
> if (ret)
> goto error;
Ah, OK. I got it. the "file->event_call" is for the eprobe's event
itself, thus the filter doesn't work. ep->event is the event of the
original event. Thus your fix is correct.
Thank you!
>
> Applying the above change seems to make it work the way I was expecting:
>
> root@...alhost:/sys/kernel/tracing# echo 'e syscalls/sys_enter_openat \
> flags_rename=$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
> >
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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