From: Masami Hiramatsu (Google) mhiramat@kernel.org

Add poll syscall support on the `hist` file. The Waiter will be waken up when the histogram is updated with POLLIN.

Currently, there is no way to wait for a specific event in userspace. So user needs to peek the `trace` periodicaly, or wait on `trace_pipe`. But it is not a good idea to peek at the `trace` for an event that randomly happens. And `trace_pipe` is not coming back until a page is filled with events.

This allows a user to wait for a specific event on the `hist` file. User can set a histogram trigger on the event which they want to monitor and poll() on its `hist` file. Since this poll() returns POLLIN, the next poll() will return soon unless a read() happens on that hist file.

NOTE: To read the hist file again, you must set the file offset to 0, but just for monitoring the event, you may not need to read the histogram.

Signed-off-by: Masami Hiramatsu (Google) mhiramat@kernel.org Reviewed-by: Tom Zanussi zanussi@kernel.org --- Changes in v7: - Reword description according to Steve's comment. - Use guard() for mutex. --- include/linux/trace_events.h | 14 ++++++++ kernel/trace/trace_events.c | 14 ++++++++ kernel/trace/trace_events_hist.c | 69 ++++++++++++++++++++++++++++++++++++-- 3 files changed, 94 insertions(+), 3 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index 2a5df5b62cfc..47caca4e7ff4 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -669,6 +669,20 @@ struct trace_event_file { atomic_t tm_ref; /* trigger-mode reference counter */ };

+#ifdef CONFIG_HIST_TRIGGERS +extern struct irq_work hist_poll_work; +extern wait_queue_head_t hist_poll_wq; + +static inline void hist_poll_wakeup(void) +{ + if (wq_has_sleeper(&hist_poll_wq)) + irq_work_queue(&hist_poll_work); +} + +#define hist_poll_wait(file, wait) \ + poll_wait(file, &hist_poll_wq, wait) +#endif + #define __TRACE_EVENT_FLAGS(name, value) \ static int __init trace_init_flags_##name(void) \ { \ diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 77e68efbd43e..e34b4a88d8ec 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -2972,6 +2972,20 @@ static bool event_in_systems(struct trace_event_call *call, return !*p || isspace(*p) || *p == ','; }

+#ifdef CONFIG_HIST_TRIGGERS +/* + * Wake up waiter on the hist_poll_wq from irq_work because the hist trigger + * may happen in any context. + */ +static void hist_poll_event_irq_work(struct irq_work *work) +{ + wake_up_all(&hist_poll_wq); +} + +DEFINE_IRQ_WORK(hist_poll_work, hist_poll_event_irq_work); +DECLARE_WAIT_QUEUE_HEAD(hist_poll_wq); +#endif + static struct trace_event_file * trace_create_new_event(struct trace_event_call *call, struct trace_array *tr) diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 9c058aa8baf3..e169f67c6088 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -5311,6 +5311,8 @@ static void event_hist_trigger(struct event_trigger_data *data,

if (resolve_var_refs(hist_data, key, var_ref_vals, true)) hist_trigger_actions(hist_data, elt, buffer, rec, rbe, key, var_ref_vals); + + hist_poll_wakeup(); }

static void hist_trigger_stacktrace_print(struct seq_file *m, @@ -5590,15 +5592,36 @@ static void hist_trigger_show(struct seq_file *m, n_entries, (u64)atomic64_read(&hist_data->map->drops)); }

+struct hist_file_data { + struct file *file; + u64 last_read; +}; + +static u64 get_hist_hit_count(struct trace_event_file *event_file) +{ + struct hist_trigger_data *hist_data; + struct event_trigger_data *data; + u64 ret = 0; + + list_for_each_entry(data, &event_file->triggers, list) { + if (data->cmd_ops->trigger_type == ETT_EVENT_HIST) { + hist_data = data->private_data; + ret += atomic64_read(&hist_data->map->hits); + } + } + return ret; +} + static int hist_show(struct seq_file *m, void *v) { + struct hist_file_data *hist_file = m->private; struct event_trigger_data *data; struct trace_event_file *event_file; int n = 0, ret = 0;

mutex_lock(&event_mutex);

- event_file = event_file_file(m->private); + event_file = event_file_file(hist_file->file); if (unlikely(!event_file)) { ret = -ENODEV; goto out_unlock; @@ -5608,6 +5631,7 @@ static int hist_show(struct seq_file *m, void *v) if (data->cmd_ops->trigger_type == ETT_EVENT_HIST) hist_trigger_show(m, data, n++); } + hist_file->last_read = get_hist_hit_count(event_file);

out_unlock: mutex_unlock(&event_mutex); @@ -5615,24 +5639,63 @@ static int hist_show(struct seq_file *m, void *v) return ret; }

+static __poll_t event_hist_poll(struct file *file, struct poll_table_struct *wait) +{ + struct trace_event_file *event_file; + struct seq_file *m = file->private_data; + struct hist_file_data *hist_file = m->private; + + guard(mutex)(&event_mutex); + + event_file = event_file_data(file); + if (!event_file) + return EPOLLERR; + + hist_poll_wait(file, wait); + + if (hist_file->last_read != get_hist_hit_count(event_file)) + return EPOLLIN | EPOLLRDNORM; + + return 0; +} + +static int event_hist_release(struct inode *inode, struct file *file) +{ + struct seq_file *m = file->private_data; + struct hist_file_data *hist_file = m->private; + + kfree(hist_file); + return tracing_single_release_file_tr(inode, file); +} + static int event_hist_open(struct inode *inode, struct file *file) { + struct hist_file_data *hist_file; int ret;

ret = tracing_open_file_tr(inode, file); if (ret) return ret;

+ hist_file = kzalloc(sizeof(*hist_file), GFP_KERNEL); + if (!hist_file) + return -ENOMEM; + hist_file->file = file; + /* Clear private_data to avoid warning in single_open() */ file->private_data = NULL; - return single_open(file, hist_show, file); + ret = single_open(file, hist_show, hist_file); + if (ret) + kfree(hist_file); + return ret; }

const struct file_operations event_hist_fops = { .open = event_hist_open, .read = seq_read, .llseek = seq_lseek, - .release = tracing_single_release_file_tr, + .release = event_hist_release, + .poll = event_hist_poll, };

#ifdef CONFIG_HIST_TRIGGERS_DEBUG

From: Masami Hiramatsu (Google) mhiramat@kernel.org

Add a testcase for poll() on hist file. This introduces a helper binary to the ftracetest, because there is no good way to reliably execute poll() on hist file.

Signed-off-by: Masami Hiramatsu (Google) mhiramat@kernel.org Reviewed-by: Shuah Khan skhan@linuxfoundation.org --- Changes in v7: - Add comm histogram filter for specifying test sleep command. --- tools/testing/selftests/ftrace/Makefile | 2 + tools/testing/selftests/ftrace/poll.c | 74 ++++++++++++++++++++ .../ftrace/test.d/trigger/trigger-hist-poll.tc | 74 ++++++++++++++++++++ 3 files changed, 150 insertions(+) create mode 100644 tools/testing/selftests/ftrace/poll.c create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc

diff --git a/tools/testing/selftests/ftrace/Makefile b/tools/testing/selftests/ftrace/Makefile index a1e955d2de4c..49d96bb16355 100644 --- a/tools/testing/selftests/ftrace/Makefile +++ b/tools/testing/selftests/ftrace/Makefile @@ -6,4 +6,6 @@ TEST_PROGS := ftracetest-ktap TEST_FILES := test.d settings EXTRA_CLEAN := $(OUTPUT)/logs/*

+TEST_GEN_PROGS = poll + include ../lib.mk diff --git a/tools/testing/selftests/ftrace/poll.c b/tools/testing/selftests/ftrace/poll.c new file mode 100644 index 000000000000..53258f7515e7 --- /dev/null +++ b/tools/testing/selftests/ftrace/poll.c @@ -0,0 +1,74 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Simple poll on a file. + * + * Copyright (c) 2024 Google LLC. + */ + +#include <errno.h> +#include <fcntl.h> +#include <poll.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> + +#define BUFSIZE 4096 + +/* + * Usage: + * poll [-I|-P] [-t timeout] FILE + */ +int main(int argc, char *argv[]) +{ + struct pollfd pfd = {.events = POLLIN}; + char buf[BUFSIZE]; + int timeout = -1; + int ret, opt; + + while ((opt = getopt(argc, argv, "IPt:")) != -1) { + switch (opt) { + case 'I': + pfd.events = POLLIN; + break; + case 'P': + pfd.events = POLLPRI; + break; + case 't': + timeout = atoi(optarg); + break; + default: + fprintf(stderr, "Usage: %s [-I|-P] [-t timeout] FILE\n", + argv[0]); + return -1; + } + } + if (optind >= argc) { + fprintf(stderr, "Error: Polling file is not specified\n"); + return -1; + } + + pfd.fd = open(argv[optind], O_RDONLY); + if (pfd.fd < 0) { + fprintf(stderr, "failed to open %s", argv[optind]); + perror("open"); + return -1; + } + + /* Reset poll by read if POLLIN is specified. */ + if (pfd.events & POLLIN) + do {} while (read(pfd.fd, buf, BUFSIZE) == BUFSIZE); + + ret = poll(&pfd, 1, timeout); + if (ret < 0 && errno != EINTR) { + perror("poll"); + return -1; + } + close(pfd.fd); + + /* If timeout happned (ret == 0), exit code is 1 */ + if (ret == 0) + return 1; + + return 0; +} diff --git a/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc b/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc new file mode 100644 index 000000000000..cbd01a71ecad --- /dev/null +++ b/tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-poll.tc @@ -0,0 +1,74 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# description: event trigger - test poll wait on histogram +# requires: set_event events/sched/sched_process_free/trigger events/sched/sched_process_free/hist +# flags: instance + +POLL=${FTRACETEST_ROOT}/poll + +if [ ! -x ${POLL} ]; then + echo "poll program is not compiled!" + exit_unresolved +fi + +EVENT=events/sched/sched_process_free/ + +# Check poll ops is supported. Before implementing poll on hist file, it +# returns soon with POLLIN | POLLOUT, but not POLLPRI. + +# This must wait >1 sec and return 1 (timeout). +set +e +${POLL} -I -t 1000 ${EVENT}/hist +ret=$? +set -e +if [ ${ret} != 1 ]; then + echo "poll on hist file is not supported" + exit_unsupported +fi + +# Test POLLIN +echo > trace +echo "hist:key=comm" > ${EVENT}/trigger +echo 1 > ${EVENT}/enable + +# This sleep command will exit after 2 seconds. +sleep 2 & +BGPID=$! +# if timeout happens, poll returns 1. +${POLL} -I -t 4000 ${EVENT}/hist +echo 0 > tracing_on + +if [ -d /proc/${BGPID} ]; then + echo "poll exits too soon" + kill -KILL ${BGPID} ||: + exit_fail +fi + +if ! grep -qw "sleep" trace; then + echo "poll exits before event happens" + exit_fail +fi + +# Test POLLPRI +echo > trace +echo 1 > tracing_on + +# This sleep command will exit after 2 seconds. +sleep 2 & +BGPID=$! +# if timeout happens, poll returns 1. +${POLL} -P -t 4000 ${EVENT}/hist +echo 0 > tracing_on + +if [ -d /proc/${BGPID} ]; then + echo "poll exits too soon" + kill -KILL ${BGPID} ||: + exit_fail +fi + +if ! grep -qw "sleep" trace; then + echo "poll exits before event happens" + exit_fail +fi + +exit_pass