From patchwork Fri Feb 8 15:12:57 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Liebler X-Patchwork-Id: 31357 Received: (qmail 126931 invoked by alias); 8 Feb 2019 15:13:06 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 126917 invoked by uid 89); 8 Feb 2019 15:13:06 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-27.6 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, RCVD_IN_DNSWL_LOW, SPF_PASS autolearn=ham version=3.3.2 spammy= X-HELO: mx0a-001b2d01.pphosted.com To: GNU C Library From: Stefan Liebler Subject: [PATCH] misc/tst-clone3: Fix waiting for exited thread. Date: Fri, 8 Feb 2019 16:12:57 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 x-cbid: 19020815-0016-0000-0000-00000254192D X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19020815-0017-0000-0000-000032AE2CD8 Message-Id: <0bffc1e1-9cde-181b-cf10-4cc3530fa9cb@linux.ibm.com> Hi, from time to time the test misc/tst-clone3 fails with an timeout. Then futex_wait is blocking. Usually ctid should be set to zero due to CLONE_CHILD_CLEARTID and the futex should be waken up. But the fail occures if the thread has already exited before ctid is set to the return value of clone(). Then futex_wait() will block as there will be nobody who wakes the futex up again. This patch initializes ctid to a known value before calling clone and the kernel is the only one who updates the value to zero after clone. If futex_wait is called then it is either waked up due to the exited thread or the futex syscall fails as *ctid_ptr is already zero instead of the specified value 1. Okay to commit? Bye Stefan ChangeLog: * sysdeps/unix/sysv/linux/tst-clone3.c (do_test): Initialize ctid with a known value and remove update of ctid after clone. (wait_tid): Adjust arguments and call futex_wait with ctid_val as assumed current value of ctid_ptr. commit 5a8f80973dbbf06a0eebc2064d2a14521c6a6131 Author: Stefan Liebler Date: Fri Feb 8 12:42:52 2019 +0100 misc/tst-clone3: Fix waiting for exited thread. From time to time the test misc/tst-clone3 fails with an timeout. Then futex_wait is blocking. Usually ctid should be set to zero due to CLONE_CHILD_CLEARTID and the futex should be waken up. But the fail occures if the thread has already exited before ctid is set to the return value of clone(). Then futex_wait() will block as there will be nobody who wakes the futex up again. This patch initializes ctid to a known value before calling clone and the kernel is the only one who updates the value to zero after clone. If futex_wait is called then it is either waked up due to the exited thread or the futex syscall fails as *ctid_ptr is already zero instead of the specified value 1. ChangeLog: * sysdeps/unix/sysv/linux/tst-clone3.c (do_test): Initialize ctid with a known value and remove update of ctid after clone. (wait_tid): Adjust arguments and call futex_wait with ctid_val as assumed current value of ctid_ptr. diff --git a/sysdeps/unix/sysv/linux/tst-clone3.c b/sysdeps/unix/sysv/linux/tst-clone3.c index aa8e718afe..ffa2056eb6 100644 --- a/sysdeps/unix/sysv/linux/tst-clone3.c +++ b/sysdeps/unix/sysv/linux/tst-clone3.c @@ -42,11 +42,11 @@ f (void *a) /* Futex wait for TID argument, similar to pthread_join internal implementation. */ -#define wait_tid(tid) \ +#define wait_tid(ctid_ptr, ctid_val) \ do { \ - __typeof (tid) __tid; \ - while ((__tid = (tid)) != 0) \ - futex_wait (&(tid), __tid); \ + __typeof (*(ctid_ptr)) __tid; \ + while ((__tid = *(ctid_ptr)) != 0) \ + futex_wait (ctid_ptr, ctid_val); \ } while (0) static inline int @@ -64,7 +64,11 @@ do_test (void) clone_flags |= CLONE_VM | CLONE_SIGHAND; /* We will used ctid to call on futex to wait for thread exit. */ clone_flags |= CLONE_CHILD_CLEARTID; - pid_t ctid, tid; + /* Initialize with a known value. ctid is set to zero by the kernel after the + cloned thread has exited. */ +#define CTID_INIT_VAL 1 + pid_t ctid = CTID_INIT_VAL; + pid_t tid; #ifdef __ia64__ extern int __clone2 (int (*__fn) (void *__arg), void *__child_stack_base, @@ -86,8 +90,7 @@ do_test (void) if (tid == -1) FAIL_EXIT1 ("clone failed: %m"); - ctid = tid; - wait_tid (ctid); + wait_tid (&ctid, CTID_INIT_VAL); return 2; }