From owner-freebsd-current@FreeBSD.ORG Sun Apr 5 17:45:39 2015 Return-Path: Delivered-To: current@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 4D0E047D; Sun, 5 Apr 2015 17:45:39 +0000 (UTC) Received: from pp1.rice.edu (proofpoint1.mail.rice.edu [128.42.201.100]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 15DBA7C1; Sun, 5 Apr 2015 17:45:38 +0000 (UTC) Received: from pps.filterd (pp1.rice.edu [127.0.0.1]) by pp1.rice.edu (8.14.5/8.14.5) with SMTP id t35Hha4B001546; Sun, 5 Apr 2015 12:45:01 -0500 Received: from mh1.mail.rice.edu (mh1.mail.rice.edu [128.42.201.20]) by pp1.rice.edu with ESMTP id 1tf8aybmdn-1; Sun, 05 Apr 2015 12:45:01 -0500 X-Virus-Scanned: by amavis-2.7.0 at mh1.mail.rice.edu, auth channel Received: from 108-254-203-201.lightspeed.hstntx.sbcglobal.net (108-254-203-201.lightspeed.hstntx.sbcglobal.net [108.254.203.201]) (using TLSv1 with cipher RC4-MD5 (128/128 bits)) (No client certificate requested) (Authenticated sender: alc) by mh1.mail.rice.edu (Postfix) with ESMTPSA id D6AEC460110; Sun, 5 Apr 2015 12:45:00 -0500 (CDT) Message-ID: <5521749C.4020408@rice.edu> Date: Sun, 05 Apr 2015 12:45:00 -0500 From: Alan Cox User-Agent: Mozilla/5.0 (X11; FreeBSD i386; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Gleb Smirnoff , David Wolfskill , current@freebsd.org Subject: Re: panic: Lock vm object not exclusively locked @ /usr/src/sys/vm/vm_page.c:2637 References: <20150405133758.GA40261@albert.catwhisker.org> <20150405154721.GO64665@FreeBSD.org> In-Reply-To: <20150405154721.GO64665@FreeBSD.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=13 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1402240000 definitions=main-1504050170 Cc: alc@FreeBSD.org 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: Sun, 05 Apr 2015 17:45:39 -0000 On 04/05/2015 10:47, Gleb Smirnoff wrote: > On Sun, Apr 05, 2015 at 06:37:58AM -0700, David Wolfskill wrote: > D> It ocurred rather late in the transition to multi-user mode, but > D> prior to starting xdm (on my laptop). > D>=20 > D> Previous (working) head/i386 for this machine was r281074. > D>=20 > D> Here's the first bit of the crashinfo (yes, I have a crash dump): > D>=20 > D> g1-254.catwhisker.org dumped core - see /var/crash/vmcore.3 > D>=20 > D> Sun Apr 5 06:18:44 PDT 2015 > D>=20 > D> FreeBSD g1-254.catwhisker.org 11.0-CURRENT FreeBSD 11.0-CURRENT #156= 1 r281106M/281106:1100067: Sun Apr 5 06:01:06 PDT 2015 root@g1-254.= catwhisker.org:/common/S4/obj/usr/src/sys/CANARY i386 > D>=20 > D> panic: Lock vm object not exclusively locked @ /usr/src/sys/vm/vm_pa= ge.c:2637 > > This is r281079. > > Since vm_page_advise() may call vm_page_dirty() in the MADV_DONTNEED ca= se, > the assertion is valid. So, looks like vm_fault_dontneed() needs W-lock= on > the first_object. > Actually, what I forgot was that vm_page_advise(MADV_FREE) clears the page's dirty field, and that is why an exclusive lock is asserted. As explained in vm_page.h, the pmap is allowed to set the dirty field to all ones without any locking. Moreover, the new "fast" path in vm_fault() sets the dirty field with only a read lock held.=20 vm_page_advise(MADV_DONTNEED) isn't really any different from the fast pa= th. Need to think a bit ... =20