From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 86A523857709 for ; Tue, 7 Nov 2023 11:44:58 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 86A523857709 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 86A523857709 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699357500; cv=none; b=EAF2Pb9aoixZHjGSEcn8cUTIDZRVGr5riKO98363H23pUsCHXlBzDBwPNFmCkyDpye4Pjj2S0UyLd6Zcbg+cn/tKOLdTcKv2c5KKoTIIKp3vfEgPbYpCaXTg2JP3pdW6vZxx9dIFNQJZBmuWk2krlicvJVsMYlGAvKv2BEsCKZY= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699357500; c=relaxed/simple; bh=yUpHHpOnEGBc2mBQ7zN/g7X0SArkFb9EbfbXBqyPCAY=; h=DKIM-Signature:MIME-Version:From:Date:Message-ID:Subject:To; b=GwCQ4roU/glhaM0904ch2XvIrg/QnqqezjmWaujwt/WzG4tvZBahEuLW11BTWO7XhYsG2WT1H7WEelXs8Ipw1u+nwHwbMIkPlGHGbpahvVgrrOYiGTlveoDJ+pgP40IoRUJi3/sGDor8Ui2F9FPaBQ4ROC9gseQhQxjUFO1LzHU= ARC-Authentication-Results: i=1; server2.sourceware.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1699357498; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=iUjPVwU0XGdh9WXdjbdA42IO69Az3h4U+NX56e+KuQw=; b=faZbihSTk5QPOWTBD9nXZ3y+tM9PObam1GRYzZYAhBIIyvuckvEKzF5UrtimydGwPskawL Zyy/OJQRgpSbtcrFiMTSmxPrRZr0bP7PEzUXQy3IZXpSuW48XW5PQL11xcKYlbePDqtC5u b7A9VT2c3qZHspBldE3/vIx295magy0= Received: from mail-yw1-f198.google.com (mail-yw1-f198.google.com [209.85.128.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-517-LqA8jKArPHqAu3IHnz2obw-1; Tue, 07 Nov 2023 06:44:49 -0500 X-MC-Unique: LqA8jKArPHqAu3IHnz2obw-1 Received: by mail-yw1-f198.google.com with SMTP id 00721157ae682-5a7cf717bacso76977957b3.1 for ; Tue, 07 Nov 2023 03:44:49 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699357488; x=1699962288; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=iUjPVwU0XGdh9WXdjbdA42IO69Az3h4U+NX56e+KuQw=; b=fGye2dXQVb4q09XHLQylaBGLffYGscHKTSecMSXiPIc/iT6Ob3phiYglzkR5349prc XC8B1k96dGb88CECkP9b9DOZn/qyE8tG6SVL/MRQRfypxiJoquhedW/ybEcaEy08xANt eQWMpk2qA3VqFT3t0hmIAcgeTwrnNkkRQpztZk+cPjeu0/RAsfF+9ExhPxaCRr/OuiZT T45xKM+QJYTGcRg6hI0FMsDe/CCBxbhpS08TgRrnzh2GfidFpgCY58WQilmTuqKIqPP6 Whs8w62UfYo8zpBx8AfTcuCcnJDDo2FKNNzCXbOyraF3DQRbGHIO9Vi8s28MnpkJAPoh of+A== X-Gm-Message-State: AOJu0Yxgh8dk3urSIr2uxNaaUVKDpHGBRKGQlYRX4F2nPL+dIbXH3z+e +Moarhk90tFTp5Z+TAAfWk8Z3HLqsvSDxJ3KQy1F6TNwMDSjzjCVgNNguADRn8sxEaYjavFMatF DS+hUW2YsLNGS3u0FahQ1fEwhB/XkY+U= X-Received: by 2002:a05:690c:d81:b0:5a8:286d:339e with SMTP id da1-20020a05690c0d8100b005a8286d339emr17820575ywb.4.1699357488679; Tue, 07 Nov 2023 03:44:48 -0800 (PST) X-Google-Smtp-Source: AGHT+IHgAgWTekvhlGUlY3/TdkIrv68WenuYBQ2gX997nFspUflm/3VJomBPApGmQX/0zfEcbp5+Cv0gFge+Z2pEknk= X-Received: by 2002:a05:690c:d81:b0:5a8:286d:339e with SMTP id da1-20020a05690c0d8100b005a8286d339emr17820564ywb.4.1699357488412; Tue, 07 Nov 2023 03:44:48 -0800 (PST) MIME-Version: 1.0 References: <11125.123110606520900751@us-mta-255.us.mimecast.lan> In-Reply-To: From: Jonathan Wakely Date: Tue, 7 Nov 2023 11:44:37 +0000 Message-ID: Subject: Re: [PATCH] libstdc++/112351 - deal with __gthread_once failure during locale init To: Richard Biener Cc: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-12.2 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Mon, 6 Nov 2023 at 12:52, Richard Biener wrote: > > On Mon, 6 Nov 2023, Jonathan Wakely wrote: > > > On Mon, 6 Nov 2023 at 11:52, Richard Biener wrote: > > > > > > The following makes the C++98 locale init path follow the way the > > > C++11 performs initialization. This way we deal with pthread_once > > > failing, falling back to non-threadsafe initialization which, given we > > > initialize from the library, should be serialized by the dynamic > > > loader already. > > > > > > Bootstrapped and tested on x86_64-unknown-linux-gnu, OK for trunk? > > > And GCC 13 branch? > > > > > > Thanks, > > > Richard. > > > > > > PR libstdc++/112351 > > > libstdc++-v3/ > > > * src/c++98/locale.cc (locale::facet::_S_get_c_locale): > > > Always perform non-threadsafe init when threadsafe init > > > failed. > > > --- > > > libstdc++-v3/src/c++98/locale.cc | 7 ++----- > > > 1 file changed, 2 insertions(+), 5 deletions(-) > > > > > > diff --git a/libstdc++-v3/src/c++98/locale.cc b/libstdc++-v3/src/c++98/locale.cc > > > index d308140bab7..e9bec1db3b6 100644 > > > --- a/libstdc++-v3/src/c++98/locale.cc > > > +++ b/libstdc++-v3/src/c++98/locale.cc > > > @@ -216,12 +216,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > > #ifdef __GTHREADS > > > if (__gthread_active_p()) > > > __gthread_once(&_S_once, _S_initialize_once); > > > - else > > > #endif > > > - { > > > - if (!_S_c_locale) > > > - _S_initialize_once(); > > > - } > > > + if (__builtin_expect (!_S_c_locale, 0)) > > > + _S_initialize_once(); > > > return _S_c_locale; > > > } > > > > > > I think this has a problem, which is handled correctly in > > src/c++11/locale_init.cc by checking _S_classic inside the > > _S_initialize_once function. > > We check _S_c_locale here (it's just a pointer) instead of in It's a __locale_struct* for glibc and int* for BSD. Hopefully it's always something pointer-ish so that works. > _S_initialize_once (), so I think the code is equivalent, no? > > > If the first call to __gthread_once does fail then _S_once will not be > > changed. We will fall through to calling _S_initialize_once directly > > (which is not thread-safe) and set _S_c_locale. > > > > The next time we call _S_initialize, __gthread_once will try to run > > again, and because _S_once was not changed, it might call > > _S_initialize_once() again, which writes to _S_c_locale again > > (possibly causing a data race). > > Ah, yeah, so in the C++11 path the check for !_S_classic in > locale::_S_initialize is redundant. But good spot. Redundant, but it avoids a call to _S_initialize_once, so probably worth it for performance. > > > I don't think the slightly different code in src/c++11/locale_init.cc > > is different in order to handle __gthread_once failing, I think it's > > different because the effects of locale::facet::_S_initialize_once() > > and locale::_S_initialize_once() are different. One is safe to call > > more than once, and the other isn't. > > > > I don't think we need to care about __gthread_once failing at all, do > > we? There are no error conditions for pthread_once, it always returns > > 0 (previous POSIX revisions said it could return EINVAL for an > > uninitialized pthread_once_t but that can't happen here as it's > > correctly initialized in src/c++11/locale.cc). Is the concern that it > > can fail for non-posix thread models? (I didn't check if any of them > > can actually fail) > > The concern is that there are actual products out that break with the > new I/O initialization in libstdc++ for GCC13+ because they have bugs. > It's easy enough to work around those by the proposed patch (plus > correction for the above issue). I suppose the comment in > locale::_S_initialize_once holds as well for the C++98 path. > > The failure mode of the product is that it overrides pthread_once > but does nothing (not even indicate failure) when its pthread_* > override mechanism isn't initialized yet. With libstdc++ from GCC13 > we now use pthread_once "too early" and fail to initialize the locale > object. > > Adjusted patch below. > > OK after another round of testing? OK, thanks. > > Thanks, > Richard. > > > From 4e3fa2f4426a5a10d189587b63e4d7298c347b01 Mon Sep 17 00:00:00 2001 > From: Richard Biener > Date: Mon, 6 Nov 2023 11:31:40 +0100 > Subject: [PATCH] libstdc++/112351 - deal with __gthread_once failure during > locale init > To: gcc-patches@gcc.gnu.org > > The following makes the C++98 locale init path follow the way the > C++11 performs initialization. This way we deal with pthread_once > failing, falling back to non-threadsafe initialization which, given we > initialize from the library, should be serialized by the dynamic > loader already. > > PR libstdc++/112351 > libstdc++-v3/ > * src/c++98/locale.cc (locale::facet::_S_initialize_once): > Check whether _S_c_locale is already initialized. > (locale::facet::_S_get_c_locale): Always perform non-threadsafe > init when threadsafe init failed. > --- > libstdc++-v3/src/c++98/locale.cc | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/libstdc++-v3/src/c++98/locale.cc b/libstdc++-v3/src/c++98/locale.cc > index d308140bab7..1ef0c394cd7 100644 > --- a/libstdc++-v3/src/c++98/locale.cc > +++ b/libstdc++-v3/src/c++98/locale.cc > @@ -206,6 +206,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > void > locale::facet::_S_initialize_once() > { > + // Need to check this because we could get called once from > + // _S_get_c_locale() when the program is single-threaded, and then again > + // (via __gthread_once) when it's multi-threaded. > + if (_S_c_locale) > + return; > + > // Initialize the underlying locale model. > _S_create_c_locale(_S_c_locale, _S_c_name); > } > @@ -216,12 +222,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > #ifdef __GTHREADS > if (__gthread_active_p()) > __gthread_once(&_S_once, _S_initialize_once); > - else > #endif > - { > - if (!_S_c_locale) > - _S_initialize_once(); > - } > + if (__builtin_expect (!_S_c_locale, 0)) > + _S_initialize_once(); > return _S_c_locale; > } > > -- > 2.35.3 >