From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9159FE92737 for ; Thu, 5 Oct 2023 14:43:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237727AbjJEOnU (ORCPT ); Thu, 5 Oct 2023 10:43:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234797AbjJEOhw (ORCPT ); Thu, 5 Oct 2023 10:37:52 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DCA1047883 for ; Thu, 5 Oct 2023 07:02:59 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 33FA6C3279C; Thu, 5 Oct 2023 12:45:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1696509916; bh=D2DTYMgh0RO67Xy0HPAXJ9Ru/RHiX/XQ4FolxCT4N4I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=e4IjdZ+JH6RXGozFQN6HeKgYEaF63eVjMFFUngpJgSnf9dyQRcqim/C8BqRxgQNah OOhFxe5CKBtOB54IjCkVkz8z/WzMyISNPzs5OLfl7Pl5x2fuz2Pt4G7RmvofBqUNLZ Bb163CWxRknvbEsZcrTDjr5Wx30RcxPNrOyMLgx9HVqxniE3kVQejYjfD3Be58mBsN ABZeDjJHdmgCl5Y9nEz+33p0q1ZigcayUnehI1S98c6VUiq2LhWnE3GdjWH3hKfmFp vaO893nanUqTaMsG0Ht9jrPIuCJW1l/1x/4rY1Sc9kIIQGbPLChh487vOlgxXPTh9P 1QPbZxZCVz+sQ== Date: Thu, 5 Oct 2023 14:45:12 +0200 From: Carlos Maiolino To: "Darrick J. Wong" Cc: Anthony Iliopoulos , linux-xfs@vger.kernel.org Subject: Re: [PATCH v1.1 6/6] libxfs: fix atomic64_t detection on x86 32-bit architectures Message-ID: <20231005124512.lwnvra7nwcsnuw5t@andromeda> References: <169454757570.3539425.3597048437340386509.stgit@frogsfrogsfrogs> <169454761010.3539425.13599600178844641233.stgit@frogsfrogsfrogs> <20230912194751.GB3415652@frogsfrogsfrogs> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230912194751.GB3415652@frogsfrogsfrogs> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Tue, Sep 12, 2023 at 12:47:51PM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong > > xfsprogs during compilation tries to detect if liburcu supports atomic > 64-bit ops on the platform it is being compiled on, and if not it falls > back to using pthread mutex locks. > > The detection logic for that fallback relies on _uatomic_link_error() > which is a link-time trick used by liburcu that will cause compilation > errors on archs that lack the required support. That only works for the > generic liburcu code though, and it is not implemented for the > x86-specific code. > > In practice this means that when xfsprogs is compiled on 32-bit x86 > archs will successfully link to liburcu for atomic ops, but liburcu does > not support atomic64_t on those archs. It indicates this during runtime > by generating an illegal instruction that aborts execution, and thus > causes various xfsprogs utils to be segfaulting. > > Fix this by requiring that unsigned longs are at least 64 bits in size, > which /usually/ means that 64-bit atomic counters are supported. We > can't simply execute the liburcu atomic64_t detection code during > configure instead of only relying on the linker error because that > doesn't work for cross-compiled packages. > > Fixes: 7448af588a2e ("libxfs: fix atomic64_t poorly for 32-bit architectures") > Reported-by: Anthony Iliopoulos > Signed-off-by: Darrick J. Wong > --- > v1.1: This time with correct commit message. > --- Reviewed-by: Carlos Maiolino Carlos > m4/package_urcu.m4 | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/m4/package_urcu.m4 b/m4/package_urcu.m4 > index ef116e0cda7..4bb2b886f06 100644 > --- a/m4/package_urcu.m4 > +++ b/m4/package_urcu.m4 > @@ -26,7 +26,11 @@ rcu_init(); > # > # Make sure that calling uatomic_inc on a 64-bit integer doesn't cause a link > # error on _uatomic_link_error, which is how liburcu signals that it doesn't > -# support atomic operations on 64-bit data types. > +# support atomic operations on 64-bit data types for its generic > +# implementation (which relies on compiler builtins). For certain archs > +# where liburcu carries its own implementation (such as x86_32), it > +# signals lack of support during runtime by emitting an illegal > +# instruction, so we also need to check CAA_BITS_PER_LONG to detect that. > # > AC_DEFUN([AC_HAVE_LIBURCU_ATOMIC64], > [ AC_MSG_CHECKING([for atomic64_t support in liburcu]) > @@ -34,8 +38,11 @@ AC_DEFUN([AC_HAVE_LIBURCU_ATOMIC64], > [ AC_LANG_PROGRAM([[ > #define _GNU_SOURCE > #include > +#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)])) > ]], [[ > long long f = 3; > + > +BUILD_BUG_ON(CAA_BITS_PER_LONG < 64); > uatomic_inc(&f); > ]]) > ], have_liburcu_atomic64=yes