From patchwork Mon Jul 31 18:05:20 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Pluzhnikov X-Patchwork-Id: 795899 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=sourceware.org (client-ip=209.132.180.131; helo=sourceware.org; envelope-from=libc-alpha-return-82573-incoming=patchwork.ozlabs.org@sourceware.org; receiver=) Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; secure) header.d=sourceware.org header.i=@sourceware.org header.b="hT6shw3b"; dkim-atps=neutral Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3xLnSZ21rwz9s0Z for ; Tue, 1 Aug 2017 04:06:06 +1000 (AEST) DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-type; q=dns; s=default; b=a3P1 9KqQOGiapHHl+9YgYa1sD3oYIQMKKRydiFrY0wfu/VWW0reUQI/4ke/Y8oKwXDtu 4Gdn/I9o2b69sty97+6pPUUQbNBudkTx+Hr0Hz9XuEi0f0FY3HLVgFmrLX/FvGf3 rOmdUPEzzx+Akm82fmBmy8lS9Vzq0oUPH4A0CyM= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-type; s=default; bh=qohm3meOm7 fkvSTzUHJnmJLv2OM=; b=hT6shw3bt6n2buOJFNI1e/MiRa4BogaV/5+V9+nBsA BrRQU4qGoP43cdjde5E8K6s4CY2LYuUQepP6LVaXutZS0eHTFZT0qicTeBfx8ChN pWvLfmM5OToKuH6E94zMz8F4Odef1lUDgw+i+wqt9m080FZvv79dUFQmUaq2IGp7 o= Received: (qmail 107592 invoked by alias); 31 Jul 2017 18:05:58 -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 107037 invoked by uid 89); 31 Jul 2017 18:05:57 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-24.7 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, RCVD_IN_DNSWL_NONE, RP_MATCHES_RCVD, SPF_PASS autolearn=ham version=3.3.2 spammy=H*M:mng, H*MI:mng, flavor, zhou X-HELO: mail-vk0-f47.google.com X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=zPr1hxTcCL6/tabJ2G1gQvKdPyaBIX/1uQKvOIicIJQ=; b=jTxCujaqZXxZyuXC7KXtUj4p9HNGXdqrMk0L4KVtuPc54cq23QBakoDP78IP5dgmmo pV5Waq56IZzqnuYWakGWwVZQvNwi5TAKlDDg0aLTOHhVByV8CgL5kna4DkK/fkUA0kE5 0jvDaY66IS1V6VPd9bfk7YWj4WT6qWvltk9g+joQRe4Lj7xKNW9i/V0XSEpOMz+aREfC TdInQQew8rl1jB0owuq5msXSbfKRaP29ivsa4sn2d/fiko0evemwTGjwEmFSQkvRUuk6 Bd2utswyPgAXgA/u9NWyP2BUeoFQpXcb9OW9hLAFFsiRcC2/GU2VsxaRj0AJByAd3Z/Y ra6Q== X-Gm-Message-State: AIVw111Bf7MzviO60jB5p3pND8ZDijubfebfpgIPq36H0Wa7hKwT7MjI upRgFlxkhdrJysrsV9aF9p6z85/vMSM8c492NQ== X-Received: by 10.31.206.133 with SMTP id e127mr6855058vkg.145.1501524351693; Mon, 31 Jul 2017 11:05:51 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1500467179.27895.55.camel@redhat.com> <1500926864.30433.42.camel@redhat.com> From: Paul Pluzhnikov Date: Mon, 31 Jul 2017 11:05:20 -0700 Message-ID: Subject: Re: [patch] Fix for bz14333 -- race between atexit() and exit() To: Torvald Riegel Cc: Andreas Schwab , Joseph Myers , GLIBC Devel , Ricky Zhou , "Carlos O'Donell" On Mon, Jul 24, 2017 at 1:14 PM, Paul Pluzhnikov wrote: >> Kind of, I guess. When you write that __exit_funcs_lock protects >> __exit_funcs, do you mean that it also protects the full list that this >> global points to? If so, please say that. > > Yes, Will do. Done. >> Does that fully remove the need for what looks like an (incorrect) >> attempt to build a concurrent list? > > Probably. Let me review these. I suspect they are no longer necessary. That is correct: the half-cooked atomic accesses are no longer necessary, since all modifications (and reads) now happen under the lock. I've removed them. 2017-07-31 Paul Pluzhnikov Ricky Zhou Anoop V Chakkalakkal [BZ #14333] * stdlib/cxa_atexit.c (__internal_atexit): Use __exit_funcs_lock. Remove atomics. (__new_exitfn): Fail registration when we finished at_exit processing. * stdlib/cxa_finalize.c (__cxa_finalize): Likewise. * stdlib/on_exit.c (__on_exit): Likewise. * stdlib/exit.c (__exit_funcs_done): New variable. (__run_exit_handlers): Use __exit_funcs_lock. * stdlib/exit.h (__exit_funcs_lock, __exit_funcs_done): New declarations. * stdlib/Makefile (test-atexit-race, test-quick_at_exit-race) (test-cxa_atexit-race): New tests. * stdlib/test-atexit-race-common.c: New. * stdlib/test-atexit-race.c: New. * stdlib/test-at_quick_exit-race.c: New. * stdlib/test-cxa_atexit-race.c: New. diff --git a/stdlib/Makefile b/stdlib/Makefile index 0314d5926b..c768b17cd4 100644 --- a/stdlib/Makefile +++ b/stdlib/Makefile @@ -80,7 +80,8 @@ tests := tst-strtol tst-strtod testmb testrand testsort testdiv \ tst-strtol-locale tst-strtod-nan-locale tst-strfmon_l \ tst-quick_exit tst-thread-quick_exit tst-width \ tst-width-stdint tst-strfrom tst-strfrom-locale \ - tst-getrandom + tst-getrandom test-atexit-race test-at_quick_exit-race \ + test-cxa_atexit-race tests-internal := tst-strtod1i tst-strtod3 tst-strtod4 tst-strtod5i \ tst-tls-atexit tst-tls-atexit-nodelete tests-static := tst-secure-getenv @@ -89,6 +90,10 @@ ifeq ($(build-hardcoded-path-in-tests),yes) tests += tst-empty-env endif +LDLIBS-test-atexit-race = $(shared-thread-library) +LDLIBS-test-at_quick_exit-race = $(shared-thread-library) +LDLIBS-test-cxa_atexit-race = $(shared-thread-library) + ifeq ($(have-cxx-thread_local),yes) CFLAGS-tst-quick_exit.o = -std=c++11 LDLIBS-tst-quick_exit = -lstdc++ diff --git a/stdlib/cxa_atexit.c b/stdlib/cxa_atexit.c index ce5d9f22b4..10b74d2982 100644 --- a/stdlib/cxa_atexit.c +++ b/stdlib/cxa_atexit.c @@ -21,21 +21,29 @@ #include #include "exit.h" -#include #include #undef __cxa_atexit +/* We change global data, so we need locking. */ +__libc_lock_define_initialized (, __exit_funcs_lock) + int attribute_hidden __internal_atexit (void (*func) (void *), void *arg, void *d, struct exit_function_list **listp) { - struct exit_function *new = __new_exitfn (listp); + struct exit_function *new; + + __libc_lock_lock (__exit_funcs_lock); + new = __new_exitfn (listp); if (new == NULL) - return -1; + { + __libc_lock_unlock (__exit_funcs_lock); + return -1; + } #ifdef PTR_MANGLE PTR_MANGLE (func); @@ -43,8 +51,8 @@ __internal_atexit (void (*func) (void *), void *arg, void *d, new->func.cxa.fn = (void (*) (void *, int)) func; new->func.cxa.arg = arg; new->func.cxa.dso_handle = d; - atomic_write_barrier (); new->flavor = ef_cxa; + __libc_lock_unlock (__exit_funcs_lock); return 0; } @@ -60,10 +68,6 @@ __cxa_atexit (void (*func) (void *), void *arg, void *d) libc_hidden_def (__cxa_atexit) -/* We change global data, so we need locking. */ -__libc_lock_define_initialized (static, lock) - - static struct exit_function_list initial; struct exit_function_list *__exit_funcs = &initial; uint64_t __new_exitfn_called; @@ -76,7 +80,10 @@ __new_exitfn (struct exit_function_list **listp) struct exit_function *r = NULL; size_t i = 0; - __libc_lock_lock (lock); + if (__exit_funcs_done) + /* exit code finished processing all handlers + so fail this registration */ + return NULL; for (l = *listp; l != NULL; p = l, l = l->next) { @@ -127,7 +134,5 @@ __new_exitfn (struct exit_function_list **listp) ++__new_exitfn_called; } - __libc_lock_unlock (lock); - return r; } diff --git a/stdlib/cxa_finalize.c b/stdlib/cxa_finalize.c index aa0a70cb58..2216a3d87e 100644 --- a/stdlib/cxa_finalize.c +++ b/stdlib/cxa_finalize.c @@ -17,7 +17,6 @@ #include #include -#include #include "exit.h" #include #include @@ -31,36 +30,35 @@ __cxa_finalize (void *d) { struct exit_function_list *funcs; + __libc_lock_lock (__exit_funcs_lock); + restart: for (funcs = __exit_funcs; funcs; funcs = funcs->next) { struct exit_function *f; for (f = &funcs->fns[funcs->idx - 1]; f >= &funcs->fns[0]; --f) - { - void (*cxafn) (void *arg, int status); - void *cxaarg; + if ((d == NULL || d == f->func.cxa.dso_handle) && f->flavor == ef_cxa) + { + const uint64_t check = __new_exitfn_called; + void (*cxafn) (void *arg, int status) = f->func.cxa.fn; + void *cxaarg = f->func.cxa.arg; - if ((d == NULL || d == f->func.cxa.dso_handle) - /* We don't want to run this cleanup more than once. */ - && (cxafn = f->func.cxa.fn, - cxaarg = f->func.cxa.arg, - ! catomic_compare_and_exchange_bool_acq (&f->flavor, ef_free, - ef_cxa))) - { - uint64_t check = __new_exitfn_called; + /* We don't want to run this cleanup more than once. */ + f->flavor = ef_free; #ifdef PTR_DEMANGLE - PTR_DEMANGLE (cxafn); + PTR_DEMANGLE (cxafn); #endif - cxafn (cxaarg, 0); + __libc_lock_unlock (__exit_funcs_lock); + cxafn (cxaarg, 0); + __libc_lock_lock (__exit_funcs_lock); - /* It is possible that that last exit function registered - more exit functions. Start the loop over. */ - if (__glibc_unlikely (check != __new_exitfn_called)) - goto restart; - } - } + /* It is possible that that last exit function registered + more exit functions. Start the loop over. */ + if (__glibc_unlikely (check != __new_exitfn_called)) + goto restart; + } } /* Also remove the quick_exit handlers, but do not call them. */ @@ -79,4 +77,5 @@ __cxa_finalize (void *d) if (d != NULL) UNREGISTER_ATFORK (d); #endif + __libc_lock_unlock (__exit_funcs_lock); } diff --git a/stdlib/exit.c b/stdlib/exit.c index c0b6d666c7..69acef5c23 100644 --- a/stdlib/exit.c +++ b/stdlib/exit.c @@ -19,11 +19,14 @@ #include #include #include +#include #include "exit.h" #include "set-hooks.h" DEFINE_HOOK (__libc_atexit, (void)) +/* Initialise the processing complete flag to false. */ +bool __exit_funcs_done = false; /* Call all functions registered with `atexit' and `on_exit', in the reverse of the order in which they were registered @@ -44,14 +47,32 @@ __run_exit_handlers (int status, struct exit_function_list **listp, the functions registered with `atexit' and `on_exit'. We call everyone on the list and use the status value in the last exit (). */ - while (*listp != NULL) + while (true) { - struct exit_function_list *cur = *listp; + struct exit_function_list *cur; + + __libc_lock_lock (__exit_funcs_lock); + + restart: + cur = *listp; + + if (cur == NULL) + { + /* Exit processing complete. We will not allow any more + atexit/on_exit registrations. */ + __exit_funcs_done = true; + __libc_lock_unlock (__exit_funcs_lock); + break; + } while (cur->idx > 0) { const struct exit_function *const f = &cur->fns[--cur->idx]; + const uint64_t new_exitfn_called = __new_exitfn_called; + + /* Unlock the list while we call into user-provided code. */ + __libc_lock_unlock (__exit_funcs_lock); switch (f->flavor) { void (*atfct) (void); @@ -83,6 +104,13 @@ __run_exit_handlers (int status, struct exit_function_list **listp, cxafct (f->func.cxa.arg, status); break; } + /* Re-lock again before looking at global state. */ + __libc_lock_lock (__exit_funcs_lock); + + if (__glibc_unlikely (new_exitfn_called != __new_exitfn_called)) + /* The last exit function, or another thread, has registered + more exit functions. Start the loop over. */ + goto restart; } *listp = cur->next; @@ -90,6 +118,8 @@ __run_exit_handlers (int status, struct exit_function_list **listp, /* Don't free the last element in the chain, this is the statically allocate element. */ free (cur); + + __libc_lock_unlock (__exit_funcs_lock); } if (run_list_atexit) diff --git a/stdlib/exit.h b/stdlib/exit.h index 7f2e679246..700163c8be 100644 --- a/stdlib/exit.h +++ b/stdlib/exit.h @@ -20,6 +20,7 @@ #include #include +#include enum { @@ -57,11 +58,26 @@ struct exit_function_list size_t idx; struct exit_function fns[32]; }; + extern struct exit_function_list *__exit_funcs attribute_hidden; extern struct exit_function_list *__quick_exit_funcs attribute_hidden; +extern uint64_t __new_exitfn_called attribute_hidden; + +/* True once all registered atexit/at_quick_exit/onexit handlers have been + called */ +extern bool __exit_funcs_done attribute_hidden; + +/* This lock protects __exit_funcs, __quick_exit_funcs, __exit_funcs_done + and __new_exitfn_called globals against simultaneous access from + atexit/on_exit/at_quick_exit in multiple threads, and also from + simultaneous access while another thread is in the middle of calling + exit handlers. See BZ#14333. Note: for lists, the entire list is + protected by this lock. */ +__libc_lock_define (extern, __exit_funcs_lock); + extern struct exit_function *__new_exitfn (struct exit_function_list **listp); -extern uint64_t __new_exitfn_called attribute_hidden; + extern void __run_exit_handlers (int status, struct exit_function_list **listp, diff --git a/stdlib/on_exit.c b/stdlib/on_exit.c index 83845e76d8..f4ede2b1a7 100644 --- a/stdlib/on_exit.c +++ b/stdlib/on_exit.c @@ -17,25 +17,30 @@ #include #include "exit.h" -#include #include /* Register a function to be called by exit. */ int __on_exit (void (*func) (int status, void *arg), void *arg) { - struct exit_function *new = __new_exitfn (&__exit_funcs); + struct exit_function *new; + + __libc_lock_lock (__exit_funcs_lock); + new = __new_exitfn (&__exit_funcs); if (new == NULL) - return -1; + { + __libc_lock_unlock (__exit_funcs_lock); + return -1; + } #ifdef PTR_MANGLE PTR_MANGLE (func); #endif new->func.on.fn = func; new->func.on.arg = arg; - atomic_write_barrier (); new->flavor = ef_on; + __libc_lock_unlock (__exit_funcs_lock); return 0; } weak_alias (__on_exit, on_exit) diff --git a/stdlib/test-at_quick_exit-race.c b/stdlib/test-at_quick_exit-race.c new file mode 100644 index 0000000000..2521a6b77c --- /dev/null +++ b/stdlib/test-at_quick_exit-race.c @@ -0,0 +1,30 @@ +/* A test for at_quick_exit/quick_exit race from bz14333. + + Copyright (C) 2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +/* This file must be run from within a directory called "stdlib". */ + +#define CALL_ATEXIT at_quick_exit (&no_op) +#define CALL_EXIT quick_exit (0) + +static void +no_op (void) +{ +} + +#include diff --git a/stdlib/test-atexit-race-common.c b/stdlib/test-atexit-race-common.c new file mode 100644 index 0000000000..c4cbd9e592 --- /dev/null +++ b/stdlib/test-atexit-race-common.c @@ -0,0 +1,62 @@ +/* Support file for atexit/exit, at_quick_exit/quick_exit, etc. race tests + from bz14333. + + Copyright (C) 2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +/* This file must be run from within a directory called "stdlib". */ + +#if !defined(CALL_EXIT) || !defined(CALL_ATEXIT) +#error Must define CALL_EXIT and CALL_ATEXIT before using this file. +#endif + +#include +#include +#include + +const size_t kNumThreads = 1024; +const size_t kNumHandlers = 1024; + +static void * +threadfunc (void *unused) +{ + size_t i; + for (i = 0; i < kNumHandlers; ++i) { + CALL_ATEXIT; + } + return NULL; +} + +static int +do_test (void) +{ + size_t i; + pthread_t thr; + pthread_attr_t attr; + + pthread_attr_init (&attr); + pthread_attr_setdetachstate (&attr, 1); + + for (i = 0; i < kNumThreads; ++i) { + pthread_create (&thr, &attr, threadfunc, NULL); + } + + CALL_EXIT; +} + +#define TEST_FUNCTION do_test +#include diff --git a/stdlib/test-atexit-race.c b/stdlib/test-atexit-race.c new file mode 100644 index 0000000000..b183ecfd7e --- /dev/null +++ b/stdlib/test-atexit-race.c @@ -0,0 +1,30 @@ +/* A test for atexit/exit race from bz14333. + + Copyright (C) 2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +/* This file must be run from within a directory called "stdlib". */ + +#define CALL_ATEXIT atexit (&no_op) +#define CALL_EXIT exit (0) + +static void +no_op (void) +{ +} + +#include diff --git a/stdlib/test-cxa_atexit-race.c b/stdlib/test-cxa_atexit-race.c new file mode 100644 index 0000000000..b86f6ce212 --- /dev/null +++ b/stdlib/test-cxa_atexit-race.c @@ -0,0 +1,34 @@ +/* A test for __cxa_atexit/exit race from bz14333. + + Copyright (C) 2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +/* This file must be run from within a directory called "stdlib". */ + +#include + +#define CALL_ATEXIT __cxa_atexit (&no_op, NULL, NULL) +#define CALL_EXIT exit (0) + +int __cxa_atexit (void (*func) (void *), void *arg, void *d); + +static void +no_op (void *ignored) +{ +} + +#include