From owner-freebsd-hackers@FreeBSD.ORG Wed Oct 1 04:46:37 2014 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id E9DDEDAC for ; Wed, 1 Oct 2014 04:46:37 +0000 (UTC) Received: from mail-lb0-x231.google.com (mail-lb0-x231.google.com [IPv6:2a00:1450:4010:c04::231]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 766478FC for ; Wed, 1 Oct 2014 04:46:37 +0000 (UTC) Received: by mail-lb0-f177.google.com with SMTP id w7so45649lbi.8 for ; Tue, 30 Sep 2014 21:46:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=U+sYvnEghbeJANflAMUJ6tmJ1Fp8PKXu1tpGfNQqqa0=; b=vsMT+NhDDhYj83Bc4FiRZZFZTU4F4+jkOyMaabTzIg68S7yxyLgLU2MWUNulO78PLZ /6MKAMWUr944odYBF2h0GP4pw6dM8pIL53qaOF/db1/GtqL4BVvrbpovUf6nmCcT8aDg SNHWicj9W/iTC9jgUpwq+QAPvspRre2CGVvXWvi2y/fhc/S+JY/tTEjRWBzMOwD4639/ ieFHfeDq+nzNDD/c4/LXKo3UorPJrVQYZkYD8pSydgxHmFIgkzhEVD+fffhjAQpOiIMY aiszY+SLd4CL62ZI4leaEj85avIh88e7mgsVWuVTVLLncQPevbjtRUce607Pd9p7zaqG kiEQ== MIME-Version: 1.0 X-Received: by 10.112.13.132 with SMTP id h4mr49310987lbc.45.1412138795339; Tue, 30 Sep 2014 21:46:35 -0700 (PDT) Received: by 10.25.21.197 with HTTP; Tue, 30 Sep 2014 21:46:35 -0700 (PDT) In-Reply-To: <20141001031553.GA14360@gta.com> References: <20141001031553.GA14360@gta.com> Date: Wed, 1 Oct 2014 00:46:35 -0400 Message-ID: Subject: Re: Kernel/Compiler bug From: Ryan Stone To: Larry Baird Content-Type: text/plain; charset=UTF-8 Cc: "freebsd-hackers@freebsd.org" X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 01 Oct 2014 04:46:38 -0000 This may not be a compiler bug. A quick look at the esp values provided in that backtrace shows that at least 7KB has been used on the stack. The stack for kernel threads is only 8KB, and a stack overflow can cause a double fault like that. My suspicion would be that without optimizations on clang uses a lot more stack space and you push over the limit. There's a kernel build option for the stack size that you could change to confirm. I believe that it's called KSTACK_PAGES. Try increasing it to 4.