From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by sourceware.org (Postfix) with ESMTPS id F11893858419; Tue, 7 Nov 2023 10:55:23 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org F11893858419 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=suse.de ARC-Filter: OpenARC Filter v1.0.0 sourceware.org F11893858419 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=2001:67c:2178:6::1c ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699354525; cv=none; b=mYFJ2npcEQI24b/D/zZVh/vlXhH1eY91BbuhlnazjDTZ/MUOBp9QGTzPweckhA/tLMc3UhpBBdRLkBDjDoLchqFdQ0ZAEeL++8TFpbQ7LXj4rdRrqGBbkr7Qsp1JqdHpjT7PHjBiy2/P7aDHmPUblyZoKxqu6UiE5/48C09WL0Y= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699354525; c=relaxed/simple; bh=xka6M2rGOs9Pc1osJkeDkVaKMRokLlLPQTzlhXbRqxA=; h=DKIM-Signature:DKIM-Signature:Date:From:To:Subject:Message-ID: MIME-Version; b=VCIdwbOjp+PKC82RnF/7pDEtQM/Z9w60RZmGEly5qSAXXie4lXivQ9SojWj7H5Q7WVhvfEA/5T3XZikU7ixMXMssfzVaMX5cA34R7pfaFcE2TDwaFGROyd3N7fy0dor/2/wYBcy+BzKZzxueXv7L+o8CBiBh2aMd4MOp8KiQwug= ARC-Authentication-Results: i=1; server2.sourceware.org Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 34035337A6; Tue, 7 Nov 2023 10:55:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1699354523; h=from:from:reply-to: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=aTr/76TFP8jhFnEoJ+IcmQ5XdjVsQNK1M+XGwQrdVWk=; b=EoNzyF0QG+40HgWR2hb2d+H3Iw6gd9U8yrLLs5357W5XeQuy8iQK13sPEbFRD5OugbsPGv gAZ6BXtSq8CZP5qKoRnkxwrtXO70AJ0ZtWUMndAvn4+Y6NVI/sjJ59e2R+SqYzLhscfGAc x1dQxXDYtx5uQz3jRRnNpLncrncJ0mg= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1699354523; h=from:from:reply-to: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=aTr/76TFP8jhFnEoJ+IcmQ5XdjVsQNK1M+XGwQrdVWk=; b=kKSUR1M+SCH4jIpBlnsdWawwSjtuDHwnVVND2+fzlXhXexnCE1TchPMTFj4YrCoEj+gSaV jugZc/elAf/Fq9AQ== Received: from wotan.suse.de (wotan.suse.de [10.160.0.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id EBD822D363; Tue, 7 Nov 2023 10:55:22 +0000 (UTC) Date: Tue, 7 Nov 2023 10:55:23 +0000 (UTC) From: Richard Biener To: Jonathan Wakely cc: gcc-patches@gcc.gnu.org, libstdc++@gcc.gnu.org Subject: Re: [PATCH] libstdc++/112351 - deal with __gthread_once failure during locale init In-Reply-To: Message-ID: References: <11125.123110606520900751@us-mta-255.us.mimecast.lan> User-Agent: Alpine 2.22 (LSU 394 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-11.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,SPF_HELO_NONE,SPF_PASS,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, 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. [.. old patch ..] > > 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. > > > 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? Bootstrapped and tested on x86_64-unknown-linux-gnu. OK? Thanks, Richard. > 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; > } > >