From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS3215 2.6.0.0/16 X-Spam-Status: No, score=-4.2 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [IPv6:2620:52:3:1:0:246e:9693:128c]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id BD5CC1F5AE for ; Mon, 26 Apr 2021 19:24:36 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id DF06B38930DE; Mon, 26 Apr 2021 19:24:35 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org DF06B38930DE DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1619465075; bh=kpq4CjG7qGvYp9rQoZAupbnx5DyBtG/NtCkjJRU+4yM=; h=References:In-Reply-To:Date:Subject:To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To: From; b=P4SAIR9Or1He4antU5wZP1xhubQoxiyZ/MytWyzpztiWB/qFmGPG7v5sA9JRg1rf9 5XLOTd5VbzTgRX9pfssvMDN2mqV9oJaFIdQCjbOq+rn+ghP9hjm3QH7oyTak33rZ8M HO12h7MVp1DifHa3u9gJ6zJbXNufwhPuscSVzgBo= Received: from mail-pj1-x1034.google.com (mail-pj1-x1034.google.com [IPv6:2607:f8b0:4864:20::1034]) by sourceware.org (Postfix) with ESMTPS id 2C13E3892035 for ; Mon, 26 Apr 2021 19:24:31 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 2C13E3892035 Received: by mail-pj1-x1034.google.com with SMTP id gq23-20020a17090b1057b0290151869af68bso5773799pjb.4 for ; Mon, 26 Apr 2021 12:24:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=SqDj4rnzuFdbg6r56s9uFF0faViua6NB6/PyZu4d07o=; b=O5wq/Nb0JKck01L1bDN7CBrctC5PPhC0cArih/Bl3mJdCeyMeW9H5cxnu4qtkTElm7 e8oeDjxGNFu+IkmrS7V8rk736XDF/+3LcLirqfBYcPP4GsrC9HcMWrrmmnwcM+GyM6BE +w0YdG+hYBfwTmgTcRZwbDXzGq619d+NVoRBcyfdUTVWyT7ETwAVybFvC9OORpsEs0TB zQ4q/JZFBU+cEBIU3mtWZI4o7zu3ULirAnwj0HSWEWZm8nomkBiHnJ2xpaWMiPfEVJI2 moltCd7UVNPoUWvdKOPJhwZsea8knAVVX11sWnSOS9M2UWKwK3obQoGNn6S4zngLESRc GrFA== X-Gm-Message-State: AOAM530oDA5CVlX9f9uUuXvFgVCATBRofJEisSGms+Smw30QgFXwPj6p Oxd+RTbLo10jJ4mGWH0Av9WNqqr/lCO7c18JRUEpNILYgJ3sDV0H X-Google-Smtp-Source: ABdhPJzLbHbHcCt8fE+aNSmFVJOM1QQj/n/b2DZzo3G1SA1ILtk19CkAZO3qJVblwc41lTGqnUAtv3m7m1P9wnVJoAk= X-Received: by 2002:a17:90a:a103:: with SMTP id s3mr23484445pjp.158.1619465069193; Mon, 26 Apr 2021 12:24:29 -0700 (PDT) MIME-Version: 1.0 References: <20210426192036.1743585-1-vitalybuka@google.com> In-Reply-To: <20210426192036.1743585-1-vitalybuka@google.com> Date: Mon, 26 Apr 2021 12:23:52 -0700 Message-ID: Subject: Re: [PATCH] stdlib: Fix data race in __run_exit_handlers To: GLIBC Devel Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Vitaly Buka via Libc-alpha Reply-To: Vitaly Buka Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" The last patch removes static cb_arg and improves description of race case 2. On Mon, 26 Apr 2021 at 12:20, Vitaly Buka wrote: > Fixes https://sourceware.org/bugzilla/show_bug.cgi?id=27749 > > Keep __exit_funcs_lock almost all the time and unlock it only to execute > callbacks. This fixed two issues. > > 1. f->func.cxa was modified outside the lock with rare data race like: > thread 0: __run_exit_handlers unlock __exit_funcs_lock > thread 1: __internal_atexit locks __exit_funcs_lock > thread 0: f->flavor = ef_free; > thread 1: sees ef_free and use it as new > thread 1: new->func.cxa.fn = (void (*) (void *, int)) func; > thread 1: new->func.cxa.arg = arg; > thread 1: new->flavor = ef_cxa; > thread 0: cxafct = f->func.cxa.fn; // it's wrong fn! > thread 0: cxafct (f->func.cxa.arg, status); // it's wrong arg! > thread 0: goto restart; > thread 0: call the same exit_function again as it's ef_cxa > > 2. Don't unlock in main while loop after *listp = cur->next. If *listp > is NULL and __exit_funcs_done is false another thread may fail in > __new_exitfn on assert (l != NULL): > thread 0: *listp = cur->next; // It can be the last: *listp = > NULL. > thread 0: __libc_lock_unlock > thread 1: __libc_lock_lock in __on_exit > thread 1: __new_exitfn > thread 1: if (__exit_funcs_done) // false: thread 0 isn't there > yet. > thread 1: l = *listp > thread 1: moves one and crashes on assert (l != NULL); > > The test needs multiple iterations to consistently fail without the fix. > --- > stdlib/Makefile | 4 +- > stdlib/exit.c | 28 ++++++--- > stdlib/test-cxa_atexit-race2.c | 109 +++++++++++++++++++++++++++++++++ > 3 files changed, 130 insertions(+), 11 deletions(-) > create mode 100644 stdlib/test-cxa_atexit-race2.c > > diff --git a/stdlib/Makefile b/stdlib/Makefile > index b3b30ab73e..f5755a1654 100644 > --- a/stdlib/Makefile > +++ b/stdlib/Makefile > @@ -81,7 +81,8 @@ tests := tst-strtol tst-strtod testmb testrand > testsort testdiv \ > tst-width-stdint tst-strfrom tst-strfrom-locale > \ > tst-getrandom tst-atexit tst-at_quick_exit > \ > tst-cxa_atexit tst-on_exit test-atexit-race > \ > - test-at_quick_exit-race test-cxa_atexit-race > \ > + test-at_quick_exit-race test-cxa_atexit-race > \ > + test-cxa_atexit-race2 > \ > test-on_exit-race test-dlclose-exit-race > \ > tst-makecontext-align test-bz22786 tst-strtod-nan-sign \ > tst-swapcontext1 tst-setcontext4 tst-setcontext5 \ > @@ -100,6 +101,7 @@ 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) > +LDLIBS-test-cxa_atexit-race2 = $(shared-thread-library) > LDLIBS-test-on_exit-race = $(shared-thread-library) > LDLIBS-tst-canon-bz26341 = $(shared-thread-library) > > diff --git a/stdlib/exit.c b/stdlib/exit.c > index bed82733ad..f095b38ab3 100644 > --- a/stdlib/exit.c > +++ b/stdlib/exit.c > @@ -45,6 +45,8 @@ __run_exit_handlers (int status, struct > exit_function_list **listp, > if (run_dtors) > __call_tls_dtors (); > > + __libc_lock_lock (__exit_funcs_lock); > + > /* We do it this way to handle recursive calls to exit () made by > the functions registered with `atexit' and `on_exit'. We call > everyone on the list and use the status value in the last > @@ -53,8 +55,6 @@ __run_exit_handlers (int status, struct > exit_function_list **listp, > { > struct exit_function_list *cur; > > - __libc_lock_lock (__exit_funcs_lock); > - > restart: > cur = *listp; > > @@ -63,7 +63,6 @@ __run_exit_handlers (int status, struct > exit_function_list **listp, > /* Exit processing complete. We will not allow any more > atexit/on_exit registrations. */ > __exit_funcs_done = true; > - __libc_lock_unlock (__exit_funcs_lock); > break; > } > > @@ -72,44 +71,52 @@ __run_exit_handlers (int status, struct > exit_function_list **listp, > struct exit_function *const f = &cur->fns[--cur->idx]; > const uint64_t new_exitfn_called = __new_exitfn_called; > > - /* Unlock the list while we call a foreign function. */ > - __libc_lock_unlock (__exit_funcs_lock); > switch (f->flavor) > { > void (*atfct) (void); > void (*onfct) (int status, void *arg); > void (*cxafct) (void *arg, int status); > + void *arg; > > case ef_free: > case ef_us: > break; > case ef_on: > onfct = f->func.on.fn; > + arg = f->func.on.arg; > #ifdef PTR_DEMANGLE > PTR_DEMANGLE (onfct); > #endif > - onfct (status, f->func.on.arg); > + /* Unlock the list while we call a foreign function. */ > + __libc_lock_unlock (__exit_funcs_lock); > + onfct (status, arg); > + __libc_lock_lock (__exit_funcs_lock); > break; > case ef_at: > atfct = f->func.at; > #ifdef PTR_DEMANGLE > PTR_DEMANGLE (atfct); > #endif > + /* Unlock the list while we call a foreign function. */ > + __libc_lock_unlock (__exit_funcs_lock); > atfct (); > + __libc_lock_lock (__exit_funcs_lock); > break; > case ef_cxa: > /* To avoid dlclose/exit race calling cxafct twice (BZ > 22180), > we must mark this function as ef_free. */ > f->flavor = ef_free; > cxafct = f->func.cxa.fn; > + arg = f->func.cxa.arg; > #ifdef PTR_DEMANGLE > PTR_DEMANGLE (cxafct); > #endif > - cxafct (f->func.cxa.arg, status); > + /* Unlock the list while we call a foreign function. */ > + __libc_lock_unlock (__exit_funcs_lock); > + cxafct (arg, status); > + __libc_lock_lock (__exit_funcs_lock); > 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 > @@ -123,9 +130,10 @@ __run_exit_handlers (int status, struct > exit_function_list **listp, > allocate element. */ > free (cur); > > - __libc_lock_unlock (__exit_funcs_lock); > } > > + __libc_lock_unlock (__exit_funcs_lock); > + > if (run_list_atexit) > RUN_HOOK (__libc_atexit, ()); > > diff --git a/stdlib/test-cxa_atexit-race2.c > b/stdlib/test-cxa_atexit-race2.c > new file mode 100644 > index 0000000000..9ab110ebaf > --- /dev/null > +++ b/stdlib/test-cxa_atexit-race2.c > @@ -0,0 +1,109 @@ > +/* Support file for atexit/exit, etc. race tests. > + Copyright (C) 2017-2021 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". */ > + > +/* The atexit/exit, at_quick_exit/quick_exit, __cxa_atexit/exit, etc. > exhibited > + data race while calling destructors. > + > + This test registers destructors from the background thread, and checks > that > + the same destructor is not called more than once. */ > + > +#include > +#include > +#include > +#include > +#include > +#include > + > +static atomic_int registered; > +static atomic_int todo = 100000; > + > +static void > +atexit_cb (void *arg) > +{ > + atomic_fetch_sub (®istered, 1); > + static void *prev; > + if (arg == prev) > + { > + printf ("%p\n", arg); > + abort (); > + } > + prev = arg; > + > + while (atomic_load (&todo) > 0 && atomic_load (®istered) < 100) > + ; > +} > + > +int __cxa_atexit (void (*func) (void *), void *arg, void *d); > + > + > +static void * > +thread_func (void *arg) > +{ > + void *cb_arg = NULL; > + while (atomic_load (&todo) > 0) > + if (atomic_load(®istered) < 10000) { > + int n = 10; > + for (int i = 0; i < n; ++i) __cxa_atexit(&atexit_cb, ++cb_arg, 0); > + atomic_fetch_add(®istered, n); > + atomic_fetch_sub(&todo, n); > + } > + return 0; > +} > + > +static void > +test_and_exit (void) > +{ > + pthread_attr_t attr; > + > + xpthread_attr_init (&attr); > + xpthread_attr_setdetachstate (&attr, 1); > + > + xpthread_create (&attr, thread_func, NULL); > + xpthread_attr_destroy (&attr); > + while (!atomic_load (®istered)) > + ; > + exit (0); > +} > + > +static int > +do_test (void) > +{ > + for (int i = 0; i < 20; ++i) > + { > + for (int i = 0; i < 10; ++i) > + if (fork () == 0) > + test_and_exit (); > + > + int status; > + while (wait (&status) > 0) > + { > + if (!WIFEXITED (status)) > + { > + printf ("Failed interation %d\n", i); > + abort (); > + } > + } > + } > + > + exit (0); > +} > + > +#define TEST_FUNCTION do_test > +#include > -- > 2.31.1.498.g6c1eba8ee3d-goog > >