4be0a1b587
Specifically, if we're waking up some value n > BATCH_SIZE, then the copyin(9) is wrong on the second iteration due to upp being the wrong type. upp is currently a uint32_t**, so upp + pos advances it by twice as many elements as it should (host pointer size vs. compat32 pointer size). Fix it by just making upp a uint32_t*; it's still technically a double pointer, but the distinction doesn't matter all that much here since we're just doing arithmetic on it. Add a test case that demonstrates the problem, placed with the libthr tests since one messing with _umtx_op should be running these tests. Running under compat32, the new test case will hang as threads after the first 128 get missed in the wake. it's not immediately clear how to hit it in practice, since pthread_cond_broadcast() uses a smaller (sleepq batch?) size observed to be around ~50 -- I did not spend much time digging into it. The uintptr_t change makes no functional difference, but i've tossed it in since it's more accurate (semantically). Reported by: Andrew Gierth (andrew_tao173.riddles.org.uk, inspection) Reviewed by: kib MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D27231
109 lines
3.1 KiB
C
109 lines
3.1 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause
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*
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* Copyright (c) 2020 Kyle Evans <kevans@FreeBSD.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <sys/umtx.h>
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#include <pthread.h>
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#include <atf-c.h>
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/*
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* This is an implementation detail of _umtx_op(2), pulled from
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* sys/kern/kern_umtx.c. The relevant bug observed that requests above the
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* batch side would not function as intended, so it's important that this
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* reflects the BATCH_SIZE configured there.
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*/
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#define UMTX_OP_BATCH_SIZE 128
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#define THREAD_COUNT ((UMTX_OP_BATCH_SIZE * 3) / 2)
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static pthread_mutex_t static_mutex = PTHREAD_MUTEX_INITIALIZER;
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static int batched_waiting;
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static void *
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batching_threadfunc(void *arg)
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{
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pthread_mutex_lock(&static_mutex);
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++batched_waiting;
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pthread_mutex_unlock(&static_mutex);
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_umtx_op(arg, UMTX_OP_WAIT_UINT_PRIVATE, 0, NULL, NULL);
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return (NULL);
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}
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ATF_TC(batching);
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ATF_TC_HEAD(batching, tc)
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{
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atf_tc_set_md_var(tc, "descr",
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"Checks batching of UMTX_OP_NWAKE_PRIVATE");
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}
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ATF_TC_BODY(batching, tc)
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{
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uintptr_t addrs[THREAD_COUNT];
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uint32_t vals[THREAD_COUNT];
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pthread_t threads[THREAD_COUNT];
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for (int i = 0; i < THREAD_COUNT; i++) {
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addrs[i] = (uintptr_t)&vals[i];
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vals[i] = 0;
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pthread_create(&threads[i], NULL, batching_threadfunc,
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&vals[i]);
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}
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pthread_mutex_lock(&static_mutex);
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while (batched_waiting != THREAD_COUNT) {
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pthread_mutex_unlock(&static_mutex);
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pthread_yield();
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pthread_mutex_lock(&static_mutex);
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}
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/*
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* Spin for another .50 seconds to make sure they're all safely in the
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* kernel.
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*/
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usleep(500000);
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pthread_mutex_unlock(&static_mutex);
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_umtx_op(addrs, UMTX_OP_NWAKE_PRIVATE, THREAD_COUNT, NULL, NULL);
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for (int i = 0; i < THREAD_COUNT; i++) {
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ATF_REQUIRE_EQ(0, pthread_join(threads[i], NULL));
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}
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}
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ATF_TP_ADD_TCS(tp)
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{
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ATF_TP_ADD_TC(tp, batching);
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return (atf_no_error());
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}
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