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/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* Copyright (c) 2026 Alexander Leidinger <netchild@FreeBSD.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other advertising materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/*
* Regression tests for detaching a process-mode PMC from a target that
* still has it loaded on hardware. The runcount reference for a live
* PMC is dropped only by the context-switch-out reclaim, which the
* scheduler gates on P_HWPMC; detaching used to clear P_HWPMC without
* draining the reference, so the following release spun forever in
* pmc_wait_for_pmc_idle() - a panic ("waiting too long for pmc to be
* free") on an INVARIANTS kernel, an unkillable loop holding the hwpmc
* lock otherwise.
*
* The failure is deterministic: attaching a counting PMC to the current
* (running) thread and detaching it before release always left the
* reference live. On a kernel that carries the fix these tests complete
* immediately; run against a kernel that lacks it they would wedge, so
* (like any hwpmc regression test) they ship alongside the fix.
*
* They need an allocatable process-mode counting event, and skip where
* none is available (hwpmc(4) not loaded, or a VM without a vPMU).
*/
#include <sys/types.h>
#include <errno.h>
#include <pmc.h>
#include <pthread.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <atf-c.h>
static const char *counting_events[] = {
"instructions",
"cycles",
"branches",
"unhalted-core-cycles",
"inst_retired.any",
"cpu_clk_unhalted.thread",
"ls_not_halted_cyc",
NULL
};
static volatile int spin_stop;
static void *
spinner(void *arg __unused)
{
volatile unsigned long s = 0;
while (spin_stop == 0)
s += 1;
return (NULL);
}
static void
burn_cpu(void)
{
volatile unsigned long s = 0;
int i;
for (i = 0; i < 1000000; i++)
s += i;
}
/* Allocate the first available process-mode counting PMC, or skip. */
static pmc_id_t
alloc_counting_pmc(void)
{
pmc_id_t id;
int i;
if (pmc_init() != 0)
atf_tc_skip("hwpmc(4) is not available: %s", strerror(errno));
for (i = 0; counting_events[i] != NULL; i++) {
id = PMC_ID_INVALID;
if (pmc_allocate(counting_events[i], PMC_MODE_TC, 0,
PMC_CPU_ANY, &id, 0) == 0)
return (id);
}
atf_tc_skip("no allocatable process-mode counting event "
"(no vPMU?)");
return (PMC_ID_INVALID); /* not reached */
}
ATF_TC(detach_live_self);
ATF_TC_HEAD(detach_live_self, tc)
{
atf_tc_set_md_var(tc, "descr",
"Detaching a running counting PMC from the current thread and "
"then releasing it does not leak its runcount reference");
atf_tc_set_md_var(tc, "require.user", "root");
}
ATF_TC_BODY(detach_live_self, tc)
{
pmc_id_t id;
id = alloc_counting_pmc();
ATF_REQUIRE(pmc_attach(id, 0) == 0); /* 0 == current process */
ATF_REQUIRE(pmc_start(id) == 0);
burn_cpu(); /* make the counter live */
/* Detach while still loaded on this CPU, then release. */
ATF_REQUIRE(pmc_detach(id, 0) == 0);
ATF_REQUIRE(pmc_release(id) == 0); /* wedged before the fix */
}
ATF_TC(detach_live_multithread);
ATF_TC_HEAD(detach_live_multithread, tc)
{
atf_tc_set_md_var(tc, "descr",
"Detaching a running process-scope counting PMC drains the "
"references held by the process' other threads");
atf_tc_set_md_var(tc, "require.user", "root");
}
ATF_TC_BODY(detach_live_multithread, tc)
{
pthread_t th[3];
pmc_id_t id;
int i, n;
id = alloc_counting_pmc();
/* Sibling threads keep the process-scope PMC live on other CPUs. */
spin_stop = 0;
for (n = 0; n < 3; n++)
ATF_REQUIRE(pthread_create(&th[n], NULL, spinner, NULL) == 0);
ATF_REQUIRE(pmc_attach(id, 0) == 0);
ATF_REQUIRE(pmc_start(id) == 0);
burn_cpu();
/* Let the siblings be scheduled and pick up the PMC. */
usleep(200 * 1000);
ATF_REQUIRE(pmc_detach(id, 0) == 0);
ATF_REQUIRE(pmc_release(id) == 0); /* must drain the siblings */
spin_stop = 1;
for (i = 0; i < n; i++)
pthread_join(th[i], NULL);
}
ATF_TP_ADD_TCS(tp)
{
ATF_TP_ADD_TC(tp, detach_live_self);
ATF_TP_ADD_TC(tp, detach_live_multithread);
return (atf_no_error());
}
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