From owner-freebsd-hackers@FreeBSD.ORG Fri Oct 3 01:54:58 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 ED065E58 for ; Fri, 3 Oct 2014 01:54:58 +0000 (UTC) Received: from mailgate.gta.com (mailgate.gta.com [199.120.225.23]) by mx1.freebsd.org (Postfix) with ESMTP id 9E7C411E for ; Fri, 3 Oct 2014 01:54:58 +0000 (UTC) Received: (qmail 27664 invoked by uid 1000); 3 Oct 2014 01:54:56 -0000 Date: Thu, 2 Oct 2014 21:54:56 -0400 From: Larry Baird To: Konstantin Belousov Subject: Re: Kernel/Compiler bug Message-ID: <20141003015456.GA27080@gta.com> References: <20141001031553.GA14360@gta.com> <20141001134044.GA57022@gta.com> <542C8C75.30007@FreeBSD.org> <20141002075537.GU26076@kib.kiev.ua> <20141002140232.GA52387@gta.com> <20141002143345.GY26076@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141002143345.GY26076@kib.kiev.ua> User-Agent: Mutt/1.5.23 (2014-03-12) Cc: "freebsd-hackers@freebsd.org" , Ryan Stone , Dimitry Andric , Bryan Drewery 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: Fri, 03 Oct 2014 01:54:59 -0000 > The easiest thing to do is to record the stack depth for kernel mode > on entry into interrupt. Interrupt handlers are usually well written > and do not consume a lot of stack. > > Look at the intr_event_handle(), which is the entry point. The mode can > be deduced from trapframe passed. The kernel stack for the thread is > described by td->td_kstack (base, i.e. bottom) and td->td_kstack_pages > (size), so the top of the stack is at td_kstack + td_kstack_size [*]. > The current stack consumption could be taken from reading %rsp register, > or you may take the address of any local variable as well. > > * - there are pcb and usermode fpu save area at the top of the stack, and > actual kernel stack top is right below fpu save area. This should not > be important for your measurements, since you are looking at how close > the %rsp gets to the bottom. This idea worked very well. Booting a GENERIC 10.1-BETA3 kernel I get a maximum stack used of 5247 bytes. This was with a minimal virtual box configuration. It would be interesting to hear about users with more exotic hardware and or configurations. Not sure if I have the KASSERT correct. Index: kern_intr.c =================================================================== --- kern_intr.c (revision 44897) +++ kern_intr.c (working copy) @@ -1386,6 +1386,12 @@ } } +static int max_kern_thread_stack; + +SYSCTL_INT(_kern, OID_AUTO, max_kern_thread_stack, CTLFLAG_RD, + &max_kern_thread_stack, 0, + "Maxiumum stack used by a kernel thread"); + /* * Main interrupt handling body. * @@ -1407,6 +1413,22 @@ td = curthread; + /* + * Check for maximum stack used bya kernel thread. + */ + if (!TRAPF_USERMODE(frame)) { + char *top = (char *)(td->td_kstack + td->td_kstack_pages * + PAGE_SIZE - 1); + char *current = (char *)&ih; + int used = top - current; + + if (used > max_kern_thread_stack) { + max_kern_thread_stack = used; + KASSERT(max_kern_thread_stack < KSTACK_PAGES * PAGE_SIZE, + "Maximum kernel thread stack exxceeded"); + } + } + /* An interrupt with no event or handlers is a stray interrupt. */ if (ie == NULL || TAILQ_EMPTY(&ie->ie_handlers)) return (EINVAL); -- ------------------------------------------------------------------------ Larry Baird Global Technology Associates, Inc. 1992-2012 | http://www.gta.com Celebrating Twenty Years of Software Innovation | Orlando, FL Email: lab@gta.com | TEL 407-380-0220