From owner-freebsd-current@FreeBSD.ORG Fri Sep 19 20:23:35 2014 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 0D1759B for ; Fri, 19 Sep 2014 20:23:35 +0000 (UTC) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id CD738668 for ; Fri, 19 Sep 2014 20:23:34 +0000 (UTC) Received: from ralph.baldwin.cx (pool-173-70-85-31.nwrknj.fios.verizon.net [173.70.85.31]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 9F2C2B976; Fri, 19 Sep 2014 16:23:33 -0400 (EDT) From: John Baldwin To: freebsd-current@freebsd.org Subject: Re: libthr and main thread stack size Date: Fri, 19 Sep 2014 15:27:25 -0400 Message-ID: <5242716.s4iaScq0Bu@ralph.baldwin.cx> User-Agent: KMail/4.10.5 (FreeBSD/10.0-STABLE; KDE/4.10.5; amd64; ; ) In-Reply-To: <20140916081324.GQ2737@kib.kiev.ua> References: <53E36E84.4060806@ivan-labs.com> <20140916081324.GQ2737@kib.kiev.ua> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Fri, 19 Sep 2014 16:23:33 -0400 (EDT) Cc: Konstantin Belousov , "Ivan A. Kosarev" X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 19 Sep 2014 20:23:35 -0000 On Tuesday, September 16, 2014 11:13:24 AM Konstantin Belousov wrote: > On Mon, Sep 15, 2014 at 03:47:41PM -0600, Justin T. Gibbs wrote: > > On Aug 8, 2014, at 5:22 AM, Konstantin Belousov > > wrote: > > > > ? > > > > > Below is the patch which adds environment variable > > > LIBPTHREAD_BIGSTACK_MAIN. Setting it to any value results in the > > > main thread stack left as is, and other threads allocate stack > > > below the area of RLIMIT_STACK. Try it. I do not want to set this > > > behaviour as default. > > > > Is there a reason this should not be the default? Looking at the > > getrlimit() page on the OpenGroup?s site they say: > > > > RLIMIT_STACK This is the maximum size of the initial thread's stack, > > in bytes. The implementation does not automatically grow the stack > > beyond this limit. If this limit is exceeded, SIGSEGV shall be > > generated for the thread. If the thread is blocking SIGSEGV, or the > > process is ignoring or catching SIGSEGV and has not made arrangements > > to use an alternate stack, the disposition of SIGSEGV shall be set to > > SIG_DFL before it is generated. > > > > Does posix say something different? > > > > I ran into this issue when debugging a segfault on Postgres when > > running an (arguably quite bogus) query that should have fit within > > both the configured stack rlimit and Postgres? configured stack limit. > > The Postgres backend is really just single threaded, but happens > > to pull in libpthread due to the threading support in some of the > > libraries it uses. The segfault definitely violates POLA. > > > > ? Justin > > I am conservative to not disturb the address space layout in single go. > If enough people test this setting, I can consider flipping the default > to the reverse. > > I am still curious why the things were done in this way, but nobody > replied. I suspect it was done out of reasons of being overly conservative in interpreting RLIMIT_STACK. I think it is quite surprising behavior though and would rather we make your option the default and implement what the Open Group says above. -- John Baldwin