From owner-freebsd-fs@FreeBSD.ORG Tue Aug 5 19:43:47 2008 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id B7D321065676 for ; Tue, 5 Aug 2008 19:43:47 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from mail.zoral.com.ua (skuns.zoral.com.ua [91.193.166.194]) by mx1.freebsd.org (Postfix) with ESMTP id 367DB8FC17 for ; Tue, 5 Aug 2008 19:43:46 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (root@deviant.kiev.zoral.com.ua [10.1.1.148]) by mail.zoral.com.ua (8.14.2/8.14.2) with ESMTP id m75JhfWc096131 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 5 Aug 2008 22:43:42 +0300 (EEST) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (kostik@localhost [127.0.0.1]) by deviant.kiev.zoral.com.ua (8.14.2/8.14.2) with ESMTP id m75JhfTo070127; Tue, 5 Aug 2008 22:43:41 +0300 (EEST) (envelope-from kostikbel@gmail.com) Received: (from kostik@localhost) by deviant.kiev.zoral.com.ua (8.14.2/8.14.2/Submit) id m75Jhfdj070126; Tue, 5 Aug 2008 22:43:41 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: deviant.kiev.zoral.com.ua: kostik set sender to kostikbel@gmail.com using -f Date: Tue, 5 Aug 2008 22:43:41 +0300 From: Kostik Belousov To: Rick Macklem Message-ID: <20080805194341.GI97161@deviant.kiev.zoral.com.ua> References: <20080805083229.GB97161@deviant.kiev.zoral.com.ua> <20080805153221.GG97161@deviant.kiev.zoral.com.ua> <20080805165114.GH97161@deviant.kiev.zoral.com.ua> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="1BXV+/FYeXhtv2WT" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i X-Spam-Status: No, score=-4.4 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on skuns.kiev.zoral.com.ua Cc: freebsd-fs@freebsd.org Subject: Re: doing vfs_hash_get when vnode locked X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 05 Aug 2008 19:43:47 -0000 --1BXV+/FYeXhtv2WT Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Aug 05, 2008 at 01:51:40PM -0400, Rick Macklem wrote: >=20 >=20 > On Tue, 5 Aug 2008, Kostik Belousov wrote: >=20 > [stuff snipped] > >>What does v_usecount mean then, if it doesn't say "I have it in use, so > >>you can't recycle it until I vrele() it"? > >It means that the vnode memory will not be freed until vrele(). > > > >But the VOP_RECLAIM may be called any time, and it requires exclusive lo= ck. > >After vnode is reclaimed, it is reassigned to the deadfs. In particular, > >VOP_RECLAIM implementation must clear v_data. > > > >For the reclaimed vnode you still hold a reference to, you can reliably > >obtain the vnode lock. > > > [stuff snipped] > >I do not know about these systems, esp. whether and how they implement > >a forced unmount. > > > Ok, I just spent a few minutes snooping around in vfs_subr.c and I think > I see the problem. vget() has called vholdl() and then=20 > v_upgrade_usecount(), which has incremented the usecount and taken the > vnode off the free list. This appears to prevent vgonel() from being > called on it for most cases, but there is still the case in vflush() > where the FORCECLOSE flag is set. Yes, exactly. >=20 > But, it seems that it is my nfs_unmount() that calls this, so I can just > delay the FORCECLOSE for this weird case. >=20 > In fact, it looks like vgonel() would call VOP_CLOSE() because v_usecount > is still non-zero (active) and that would block during the recovery in my > code, anyhow. But, what guarantees that the vnode would not be reclaimed before/under your vref() it ? For instance, what if the vnode is locked due to reclaim being in progress ? --1BXV+/FYeXhtv2WT Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEUEARECAAYFAkiYrW0ACgkQC3+MBN1Mb4i3gwCXdpeU8gvT1AGkKgT2Eh2lGHcQ gACg7k7+/cXzve/72UvEDJlIfCy1ENs= =asfp -----END PGP SIGNATURE----- --1BXV+/FYeXhtv2WT--