Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755548AbZJ0Acf (ORCPT ); Mon, 26 Oct 2009 20:32:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755350AbZJ0Acf (ORCPT ); Mon, 26 Oct 2009 20:32:35 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:38309 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755297AbZJ0Ace (ORCPT ); Mon, 26 Oct 2009 20:32:34 -0400 Message-ID: <4AE63FA3.8040208@us.ibm.com> Date: Mon, 26 Oct 2009 17:32:35 -0700 From: Darren Hart User-Agent: Thunderbird 2.0.0.23 (X11/20090817) MIME-Version: 1.0 To: "lkml, " , Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Eric Dumazet , Dinakar Guniguntala , "Stultz, John" Subject: Re: [PATCH] RFC: futex: make futex_lock_pi interruptible References: <4AE63E3D.8030903@us.ibm.com> In-Reply-To: <4AE63E3D.8030903@us.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6728 Lines: 244 Darren Hart wrote: > From 9ea67856951c87a03a5177e1382d836622642521 Mon Sep 17 00:00:00 2001 > From: Darren Hart > Date: Mon, 26 Oct 2009 17:15:54 -0700 > Subject: [PATCH] RFC: futex: make futex_lock_pi interruptible > The following C test case demonstrates how this patch could be used to implement interruptible locking. There is an awful lot of debug code and some other relics of a hacked together test in there now, but if anyone wanted to test the futex changes, this will do the trick. /****************************************************************************** * * Copyright ? International Business Machines Corp., 2009 * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See * the GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA * * NAME * mutexint.c * * DESCRIPTION * Provide an interruptible PI-aware locking construct. * * AUTHOR * Darren Hart * * HISTORY * 2009-Oct-26: Initial version by Darren Hart * *****************************************************************************/ #include #include #include #include #include #include #include /* * The futex() call has been removed from the include/futex.h header, implement * our own version. */ //#define SYS_futex 202 #define FUTEX_PRIVATE 128 #define FUTEX_INTERRUPTIBLE 512 #define futex(uaddr, op, val, timeout, uaddr2, val3) \ syscall(SYS_futex, uaddr, op, val, timeout, uaddr2, val3) #define futex_lock_pi(uaddr, val, timeout) \ futex(uaddr, FUTEX_LOCK_PI|FUTEX_INTERRUPTIBLE|FUTEX_PRIVATE, \ val, timeout, NULL, 0) #define futex_unlock_pi(uaddr, val) \ futex(uaddr, FUTEX_UNLOCK_PI|FUTEX_PRIVATE, val, NULL, NULL, 0) #define gettid() syscall(SYS_gettid) #define SIGMUTEXINT SIGRTMIN /* * Implement cmpxchg using gcc atomic builtins. * http://gcc.gnu.org/onlinedocs/gcc-4.1.0/gcc/Atomic-Builtins.html */ static inline int cmpxchg(volatile int32_t *addr, int32_t old, int32_t new) { return __sync_val_compare_and_swap(addr, old, new); } struct mutexint { volatile int32_t lock_val; }; struct mutexint_attr { /* placeholder for future expansion */ u_int32_t flags; }; void sigmutexint_handler(int signo) { printf("handled cancel signal: %d\n", signo); } int mutexint_init(struct mutexint *mutex, struct mutexint_attr *attr) { mutex->lock_val = 0; /* future: process attr->flags */ return 0; } int mutexint_lock(struct mutexint *mutex) { int32_t val; int ret = 0; pid_t tid = gettid(); printf("%s: initial lock_val: 0x%x\n", __FUNCTION__, mutex->lock_val); if ((val = cmpxchg(&mutex->lock_val, 0, tid)) != 0) { printf("\tfirst cmpxchg old_val: 0x%x lock_val: 0x%x\n", val, mutex->lock_val); do { printf("\tdo cmpxchg old_val: 0x%x\n", val); if ((val & FUTEX_WAITERS) || (val = cmpxchg(&mutex->lock_val, val, val | FUTEX_WAITERS))) { printf("\tinner cmpxchg old_val: 0x%x lock_val: 0x%x\n", val, mutex->lock_val); printf("\tcalling futex_lock_pi:\n"); printf("\top: 0x%x\n", FUTEX_LOCK_PI | FUTEX_PRIVATE | FUTEX_INTERRUPTIBLE); printf("\t&lock_val: %p\n", &mutex->lock_val); ret = futex_lock_pi(&mutex->lock_val, val, NULL); if (ret == -1) { ret = -errno; printf("futex_lock_pi returned -1, errno is %d\n", ret); } /* * If -EINTR is returned, the lock may no longer * have owners, but we have no good way to detect that. */ printf("\tfutex_lock_pi returned. ret=%d lock_val=0x%x\n", ret, mutex->lock_val); if (ret != -EWOULDBLOCK) break; } } while ((val = cmpxchg(&mutex->lock_val, 0, tid)) != 0); } /* * Catch the case where futex_lock_pi() returns EWOULDBLOCK, but the * while conditional acquires the lock atomically and reset ret. */ if ((val & ~FUTEX_WAITERS) == tid) ret = 0; printf("%s: returning: %d\n", __FUNCTION__, ret); return ret; } int mutexint_unlock(struct mutexint *mutex) { int32_t val; int ret = 0; pid_t tid = gettid(); if ((val = cmpxchg(&mutex->lock_val, tid, 0)) != 0) { ret = futex_unlock_pi(&mutex->lock_val, val); } return ret; } int mutexint_interrupt(pthread_t pthread, struct mutexint *mutex) { /* * FIXME: return -EINVAL if the pthread is blocked on a different * thread ? */ return pthread_kill(pthread, SIGMUTEXINT); } int mutexint_prepare() { struct sigaction sa; sa.sa_handler = sigmutexint_handler; sigemptyset(&sa.sa_mask); sa.sa_flags = 0; if (sigaction(SIGMUTEXINT, &sa, NULL)) { perror("sigaction"); return 1; } return 0; } /* unit test */ #define UNIT_TEST 1 #ifdef UNIT_TEST struct mutexint mutex; void *child_thread(void *arg) { int ret; mutexint_prepare(); printf("\tchild acquiring the mutex (will block)\n"); ret = mutexint_lock(&mutex); printf("\tchild returned %d\n", ret); *(int *)arg = ret; return NULL; } int main(int argc, char *argv[]) { struct mutexint_attr m_attr; pthread_t child; int child_ret; int ret = 0; /* prepare the mutex, ensuring we use PROCESS_PRIVATE */ mutexint_init(&mutex, &m_attr); printf("\nTesting canceled mutex lock scenario.\n"); printf("\tmain() acquiring the mutex\n"); mutexint_lock(&mutex); /* prepare and start the child thread */ ret = pthread_create(&child, NULL, child_thread, &child_ret); if (ret) { perror("Failed to create pthread"); return ret; } /* ensure the child has blocked on the lock */ sleep(3); /* cancel the child thread blocking on the mutex */ printf("\tmain() canceling the child\n"); ret = mutexint_interrupt(child, &mutex); printf("\tmain() pthread_kill returned %d\n", ret); pthread_join(child, NULL); printf("Result: %s\n", child_ret == -EINTR ? "PASS" : "FAIL"); return ret; } #endif -- Darren Hart IBM Linux Technology Center Real-Time Linux Team -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/