From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Weinberger Subject: Re: [PATCH] fs: Detect API misuse of i_op->lookup Date: Sun, 25 Jan 2015 23:20:53 +0100 Message-ID: <54C56C45.6060802@nod.at> References: <1422223060-8561-1-git-send-email-richard@nod.at> <20150125221643.GK29656@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Al Viro Return-path: In-Reply-To: <20150125221643.GK29656@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Am 25.01.2015 um 23:16 schrieb Al Viro: > On Sun, Jan 25, 2015 at 10:57:40PM +0100, Richard Weinberger wrote: >> Hunting down a refcount issue in an out-of-tree filesystem uncovered >> that its lookup function directly returned the dentry which was passed to it. >> Add a BUG_ON() to detect such misuse in future. > > In principle, it's not a bug. You *must* grab a reference to dentry before > returning it, but you can very well decide to return the one you've got - > any place where have ->lookup() return NULL has every right to become > return dget(dentry). Thanks for the clarification! The filesystem in question did of course not grab a reference before returning the same dentry. Thanks, //richard