From owner-freebsd-bugs@freebsd.org Fri Feb 16 21:44:39 2018 Return-Path: Delivered-To: freebsd-bugs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 03FFAF15183 for ; Fri, 16 Feb 2018 21:44:39 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mxrelay.ysv.freebsd.org (mxrelay.ysv.freebsd.org [IPv6:2001:1900:2254:206a::19:3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "mxrelay.ysv.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 95F0D73FE2 for ; Fri, 16 Feb 2018 21:44:38 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2001:1900:2254:206a::16:76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.ysv.freebsd.org (Postfix) with ESMTPS id E1BDC118BB for ; Fri, 16 Feb 2018 21:44:37 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id w1GLibC0006768 for ; Fri, 16 Feb 2018 21:44:37 GMT (envelope-from bugzilla-noreply@freebsd.org) Received: (from www@localhost) by kenobi.freebsd.org (8.15.2/8.15.2/Submit) id w1GLib9R006767 for freebsd-bugs@FreeBSD.org; Fri, 16 Feb 2018 21:44:37 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 225960] zfs: g_access leak when unmounting UFS on a zvol Date: Fri, 16 Feb 2018 21:44:37 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Some People X-Bugzilla-Who: avg@FreeBSD.org X-Bugzilla-Status: Open X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: freebsd-bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 16 Feb 2018 21:44:39 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D225960 --- Comment #5 from Andriy Gapon --- I now think that this could be a / the deep problem in GEOM. The problem is that g_access() must be called with the GEOM topology lock h= eld. And that gives a false impression that the lock is indeed held across the c= all. But this isn't true because many classes, ZVOL being one of the many, need = to perform I/O in their access method. So, they must drop and pick up the topology lock. That, of course, can break many assumptions. Specifically, looking at g_slice_access() we can see that the code assumes = that all invocations are serialized. Indeed, if another call to g_slice_access(= ) is permitted while the consumer's access bits are not updated yet, then the following condition can be true multiple times: /* On first open, grab an extra "exclusive" bit */ if (cp->acr =3D=3D 0 && cp->acw =3D=3D 0 && cp->ace =3D=3D 0) de++; And if that ever happens and we have extra grabs on cp->ace, then the follo= wing condition will never be true (because cp->ace + de > 1): /* ... and let go of it on last close */ if ((cp->acr + dr) =3D=3D 0 && (cp->acw + dw) =3D=3D 0 && (cp->ace = + de) =3D=3D 1) de--; --=20 You are receiving this mail because: You are the assignee for the bug.=