Re: [PATCH 4/5] perf tools: Propagate error info from tp_format

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, Sep 07, 2015 at 10:38:06AM +0200, Jiri Olsa escreveu:
> Propagate error info from tp_format via ERR_PTR to get
> it all the way down to the parse-event.c tracepoint adding
> routines. Following functions now return pointer with
> encoded error:
>   - tp_format
>   - trace_event__tp_format
>   - perf_evsel__newtp_idx
>   - perf_evsel__newtp
> 
> This affects several other places in perf, that cannot use
> pointer check anymore, but must utilize the err.h interface,
> when getting error information from above functions list.

Right, so this is tricky and we must be careful, see below...
 
> Link: http://lkml.kernel.org/n/tip-bzdckgv1zfp2y8up9l7ojt7y@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  tools/perf/builtin-trace.c                  | 19 +++++++++++--------
>  tools/perf/tests/evsel-tp-sched.c           | 10 ++++++++--
>  tools/perf/tests/openat-syscall-all-cpus.c  |  3 ++-
>  tools/perf/tests/openat-syscall-tp-fields.c |  3 ++-
>  tools/perf/tests/openat-syscall.c           |  3 ++-
>  tools/perf/util/evlist.c                    |  3 ++-
>  tools/perf/util/evsel.c                     | 11 +++++++++--
>  tools/perf/util/evsel.h                     |  3 +++
>  tools/perf/util/parse-events.c              |  6 +++---
>  tools/perf/util/trace-event.c               | 13 +++++++++++--
>  10 files changed, 53 insertions(+), 21 deletions(-)
> 
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 215653274102..93b80f12f35e 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -38,6 +38,7 @@
>  #include <stdlib.h>
>  #include <sys/mman.h>
>  #include <linux/futex.h>
> +#include <linux/err.h>
>  
>  /* For older distros: */
>  #ifndef MAP_STACK
> @@ -245,13 +246,14 @@ static struct perf_evsel *perf_evsel__syscall_newtp(const char *direction, void
>  	struct perf_evsel *evsel = perf_evsel__newtp("raw_syscalls", direction);
>  
>  	/* older kernel (e.g., RHEL6) use syscalls:{enter,exit} */
> -	if (evsel == NULL)
> +	if (IS_ERR(evsel))
>  		evsel = perf_evsel__newtp("syscalls", direction);
>  
> -	if (evsel) {
> -		if (perf_evsel__init_syscall_tp(evsel, handler))
> -			goto out_delete;
> -	}
> +	if (IS_ERR(evsel))
> +		return NULL;
> +
> +	if (perf_evsel__init_syscall_tp(evsel, handler))
> +		goto out_delete;

This kind of stuff is ok, as evsel is a local variable and you kept the
interface for perf_evsel__syscall_newtp(), i.e. it returns NULL if a new
evsel can't be instantiated.

Ok, but that is a different interface than the one used by
perf_evsel__newtp(), that also instantiates a new evsel.

So when one thinks about "foo__new()" we now need to check which one of
the two interfaces it uses, if err.h or if the old NULL based failure
reporting one.

Double tricky if it is foo__new() and foo__new_variant(), as
perf_evsel__syscall_newtp() and perf_evsel__newtp(), i.e. both will
return a "struct perf_evsel" instance, but one using err.h, the other
use NULL.

Ok, you marked the ones using a comment, wonder if we couldn't use
'sparse' somehow here, is it used to check IS_ERR() usage in the kernel?

Ah, but what about this in trace__event_handler() in builtin-trace.c?
 
        if (evsel->tp_format) {
                event_format__fprintf(evsel->tp_format, sample->cpu,
                                      sample->raw_data, sample->raw_size,
                                      trace->output);
        }


Don't we have to use IS_ERR() here? Ok, no, because if setting up
evsel->tp_format fails, then that evsel will be destroyed and
perf_evsel__newtp() will return ERR_PTR(), so it is ok not no use
ERR_PTR(evsel->tp_format) because it will only be != NULL when it was
successfully set up.

But then, in perf_evsel__newtp_idx if zalloc() fails we will not return
ERR_PTR(), but instead NULL, a-ha, this one seems to be a real bug, no?

/*
 * Returns pointer with encoded error via <linux/err.h> interface.
 */
struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int idx)
{
	struct perf_evsel *evsel = zalloc(perf_evsel__object.size);
	int err = -ENOMEM;

	if (evsel != NULL) {
		struct perf_event_attr attr = {
			.type	       = PERF_TYPE_TRACEPOINT,
			.sample_type   = (PERF_SAMPLE_RAW | PERF_SAMPLE_TIME |
					  PERF_SAMPLE_CPU | PERF_SAMPLE_PERIOD),
		};

		if (asprintf(&evsel->name, "%s:%s", sys, name) < 0)
			goto out_free;

		evsel->tp_format = trace_event__tp_format(sys, name);
		if (IS_ERR(evsel->tp_format)) {
			err = PTR_ERR(evsel->tp_format);
			goto out_free;
		}

		event_attr_init(&attr);
		attr.config = evsel->tp_format->id;
		attr.sample_period = 1;
		perf_evsel__init(evsel, &attr, idx);
	}

	return evsel;

out_free:
	zfree(&evsel->name);
	free(evsel);
	return ERR_PTR(err);
}

>  
>  	return evsel;
>  
> @@ -1705,12 +1707,12 @@ static int trace__read_syscall_info(struct trace *trace, int id)
>  	snprintf(tp_name, sizeof(tp_name), "sys_enter_%s", sc->name);
>  	sc->tp_format = trace_event__tp_format("syscalls", tp_name);
>  
> -	if (sc->tp_format == NULL && sc->fmt && sc->fmt->alias) {
> +	if (IS_ERR(sc->tp_format) && sc->fmt && sc->fmt->alias) {
>  		snprintf(tp_name, sizeof(tp_name), "sys_enter_%s", sc->fmt->alias);
>  		sc->tp_format = trace_event__tp_format("syscalls", tp_name);
>  	}
>  
> -	if (sc->tp_format == NULL)
> +	if (IS_ERR(sc->tp_format))
>  		return -1;
>  
>  	sc->args = sc->tp_format->format.fields;
> @@ -2390,7 +2392,8 @@ static size_t trace__fprintf_thread_summary(struct trace *trace, FILE *fp);
>  static bool perf_evlist__add_vfs_getname(struct perf_evlist *evlist)
>  {
>  	struct perf_evsel *evsel = perf_evsel__newtp("probe", "vfs_getname");
> -	if (evsel == NULL)
> +
> +	if (IS_ERR(evsel))
>  		return false;
>  
>  	if (perf_evsel__field(evsel, "pathname") == NULL) {
> diff --git a/tools/perf/tests/evsel-tp-sched.c b/tools/perf/tests/evsel-tp-sched.c
> index 52162425c969..790e413d9a1f 100644
> --- a/tools/perf/tests/evsel-tp-sched.c
> +++ b/tools/perf/tests/evsel-tp-sched.c
> @@ -1,3 +1,4 @@
> +#include <linux/err.h>
>  #include <traceevent/event-parse.h>
>  #include "evsel.h"
>  #include "tests.h"
> @@ -36,8 +37,8 @@ int test__perf_evsel__tp_sched_test(void)
>  	struct perf_evsel *evsel = perf_evsel__newtp("sched", "sched_switch");
>  	int ret = 0;
>  
> -	if (evsel == NULL) {
> -		pr_debug("perf_evsel__new\n");
> +	if (IS_ERR(evsel)) {
> +		pr_debug("perf_evsel__newtp failed with %ld\n", PTR_ERR(evsel));
>  		return -1;
>  	}
>  
> @@ -66,6 +67,11 @@ int test__perf_evsel__tp_sched_test(void)
>  
>  	evsel = perf_evsel__newtp("sched", "sched_wakeup");
>  
> +	if (IS_ERR(evsel)) {
> +		pr_debug("perf_evsel__newtp failed with %ld\n", PTR_ERR(evsel));
> +		return -1;
> +	}
> +
>  	if (perf_evsel__test_field(evsel, "comm", 16, true))
>  		ret = -1;
>  
> diff --git a/tools/perf/tests/openat-syscall-all-cpus.c b/tools/perf/tests/openat-syscall-all-cpus.c
> index 495d8126b722..9e104a2e973d 100644
> --- a/tools/perf/tests/openat-syscall-all-cpus.c
> +++ b/tools/perf/tests/openat-syscall-all-cpus.c
> @@ -1,4 +1,5 @@
>  #include <api/fs/fs.h>
> +#include <linux/err.h>
>  #include "evsel.h"
>  #include "tests.h"
>  #include "thread_map.h"
> @@ -31,7 +32,7 @@ int test__openat_syscall_event_on_all_cpus(void)
>  	CPU_ZERO(&cpu_set);
>  
>  	evsel = perf_evsel__newtp("syscalls", "sys_enter_openat");
> -	if (evsel == NULL) {
> +	if (IS_ERR(evsel)) {
>  		tracing_path__strerror_open_tp(errno, errbuf, sizeof(errbuf), "syscalls", "sys_enter_openat");
>  		pr_err("%s\n", errbuf);
>  		goto out_thread_map_delete;
> diff --git a/tools/perf/tests/openat-syscall-tp-fields.c b/tools/perf/tests/openat-syscall-tp-fields.c
> index 01a19626c846..473d3869727e 100644
> --- a/tools/perf/tests/openat-syscall-tp-fields.c
> +++ b/tools/perf/tests/openat-syscall-tp-fields.c
> @@ -1,3 +1,4 @@
> +#include <linux/err.h>
>  #include "perf.h"
>  #include "evlist.h"
>  #include "evsel.h"
> @@ -30,7 +31,7 @@ int test__syscall_openat_tp_fields(void)
>  	}
>  
>  	evsel = perf_evsel__newtp("syscalls", "sys_enter_openat");
> -	if (evsel == NULL) {
> +	if (IS_ERR(evsel)) {
>  		pr_debug("%s: perf_evsel__newtp\n", __func__);
>  		goto out_delete_evlist;
>  	}
> diff --git a/tools/perf/tests/openat-syscall.c b/tools/perf/tests/openat-syscall.c
> index 08ac9d94a050..7b1db8306098 100644
> --- a/tools/perf/tests/openat-syscall.c
> +++ b/tools/perf/tests/openat-syscall.c
> @@ -1,4 +1,5 @@
>  #include <api/fs/tracing_path.h>
> +#include <linux/err.h>
>  #include "thread_map.h"
>  #include "evsel.h"
>  #include "debug.h"
> @@ -19,7 +20,7 @@ int test__openat_syscall_event(void)
>  	}
>  
>  	evsel = perf_evsel__newtp("syscalls", "sys_enter_openat");
> -	if (evsel == NULL) {
> +	if (IS_ERR(evsel)) {
>  		tracing_path__strerror_open_tp(errno, errbuf, sizeof(errbuf), "syscalls", "sys_enter_openat");
>  		pr_err("%s\n", errbuf);
>  		goto out_thread_map_delete;
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index d51a5200c8af..3cb2bf9bd4bd 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -25,6 +25,7 @@
>  #include <linux/bitops.h>
>  #include <linux/hash.h>
>  #include <linux/log2.h>
> +#include <linux/err.h>
>  
>  static void perf_evlist__mmap_put(struct perf_evlist *evlist, int idx);
>  static void __perf_evlist__munmap(struct perf_evlist *evlist, int idx);
> @@ -265,7 +266,7 @@ int perf_evlist__add_newtp(struct perf_evlist *evlist,
>  {
>  	struct perf_evsel *evsel = perf_evsel__newtp(sys, name);
>  
> -	if (evsel == NULL)
> +	if (IS_ERR(evsel))
>  		return -1;
>  
>  	evsel->handler = handler;
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 771ade4d5966..08c20ee4e27d 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -13,6 +13,7 @@
>  #include <traceevent/event-parse.h>
>  #include <linux/hw_breakpoint.h>
>  #include <linux/perf_event.h>
> +#include <linux/err.h>
>  #include <sys/resource.h>
>  #include "asm/bug.h"
>  #include "callchain.h"
> @@ -225,9 +226,13 @@ struct perf_evsel *perf_evsel__new_idx(struct perf_event_attr *attr, int idx)
>  	return evsel;
>  }
>  
> +/*
> + * Returns pointer with encoded error via <linux/err.h> interface.
> + */
>  struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int idx)
>  {
>  	struct perf_evsel *evsel = zalloc(perf_evsel__object.size);
> +	int err = -ENOMEM;
>  
>  	if (evsel != NULL) {
>  		struct perf_event_attr attr = {
> @@ -240,8 +245,10 @@ struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int
>  			goto out_free;
>  
>  		evsel->tp_format = trace_event__tp_format(sys, name);
> -		if (evsel->tp_format == NULL)
> +		if (IS_ERR(evsel->tp_format)) {
> +			err = PTR_ERR(evsel->tp_format);
>  			goto out_free;
> +		}
>  
>  		event_attr_init(&attr);
>  		attr.config = evsel->tp_format->id;
> @@ -254,7 +261,7 @@ struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int
>  out_free:
>  	zfree(&evsel->name);
>  	free(evsel);
> -	return NULL;
> +	return ERR_PTR(err);
>  }
>  
>  const char *perf_evsel__hw_names[PERF_COUNT_HW_MAX] = {
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 298e6bbca200..b6e8ff876f17 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -161,6 +161,9 @@ static inline struct perf_evsel *perf_evsel__new(struct perf_event_attr *attr)
>  
>  struct perf_evsel *perf_evsel__newtp_idx(const char *sys, const char *name, int idx);
>  
> +/*
> + * Returns pointer with encoded error via <linux/err.h> interface.
> + */
>  static inline struct perf_evsel *perf_evsel__newtp(const char *sys, const char *name)
>  {
>  	return perf_evsel__newtp_idx(sys, name, 0);
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index 1b284b8ad243..c47831c47220 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -1,4 +1,5 @@
>  #include <linux/hw_breakpoint.h>
> +#include <linux/err.h>
>  #include "util.h"
>  #include "../perf.h"
>  #include "evlist.h"
> @@ -393,11 +394,10 @@ static int add_tracepoint(struct list_head *list, int *idx,
>  	struct perf_evsel *evsel;
>  
>  	evsel = perf_evsel__newtp_idx(sys_name, evt_name, (*idx)++);
> -	if (!evsel)
> -		return -ENOMEM;
> +	if (IS_ERR(evsel))
> +		return PTR_ERR(evsel);
>  
>  	list_add_tail(&evsel->node, list);
> -
>  	return 0;
>  }
>  
> diff --git a/tools/perf/util/trace-event.c b/tools/perf/util/trace-event.c
> index 2f4996ab313d..8e3a60e3e15f 100644
> --- a/tools/perf/util/trace-event.c
> +++ b/tools/perf/util/trace-event.c
> @@ -7,6 +7,7 @@
>  #include <sys/stat.h>
>  #include <fcntl.h>
>  #include <linux/kernel.h>
> +#include <linux/err.h>
>  #include <traceevent/event-parse.h>
>  #include <api/fs/tracing_path.h>
>  #include "trace-event.h"
> @@ -66,6 +67,9 @@ void trace_event__cleanup(struct trace_event *t)
>  	pevent_free(t->pevent);
>  }
>  
> +/*
> + * Returns pointer with encoded error via <linux/err.h> interface.
> + */
>  static struct event_format*
>  tp_format(const char *sys, const char *name)
>  {
> @@ -74,12 +78,14 @@ tp_format(const char *sys, const char *name)
>  	char path[PATH_MAX];
>  	size_t size;
>  	char *data;
> +	int err;
>  
>  	scnprintf(path, PATH_MAX, "%s/%s/%s/format",
>  		  tracing_events_path, sys, name);
>  
> -	if (filename__read_str(path, &data, &size))
> -		return NULL;
> +	err = filename__read_str(path, &data, &size);
> +	if (err)
> +		return ERR_PTR(err);
>  
>  	pevent_parse_format(pevent, &event, data, size, sys);
>  
> @@ -87,6 +93,9 @@ tp_format(const char *sys, const char *name)
>  	return event;
>  }
>  
> +/*
> + * Returns pointer with encoded error via <linux/err.h> interface.
> + */
>  struct event_format*
>  trace_event__tp_format(const char *sys, const char *name)
>  {
> -- 
> 2.4.3