From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from birdy.pmhahn.de (birdy.pmhahn.de [88.198.22.186]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6D1FC18A6D4; Wed, 27 May 2026 14:08:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=88.198.22.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779890906; cv=none; b=C5J17RtsMBwOPij5WZ4gmTBi5gGc55eELL+vxRLyyG8YNMHF2J+YbUutDyKitpUztHf4oUrqvS1G0EwZjy8vdMYxYKEmKyhspOOpKXb75S1DbhdshEVqgEjlo4nvZDvfgCOhT/1WLEMBG6dDmd5ZaZO2o7utSnWCG6d0LH7lIts= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779890906; c=relaxed/simple; bh=rnvPlY7SKQat4XqjTKrPe6m37pte20Tp9Jd5r0LlGbQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=r/3Xz7SSozAOC1Lk/fz9C1ursCRoOrPjdj52JvaSzy0aQnkyPyvcWx0yuXmcG6wy79N7sWG04FFXmbkp/c+IhfoTqbiaBW2m1xQVMJtcF2ckCowUqukMyvlo0MgjokuTyO2PPLcsTg5r2b9SU5ZJvqUb4Ph0hOLlieD3/TTiW4c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=pmhahn.de; spf=pass smtp.mailfrom=pmhahn.de; dkim=fail (2048-bit key) header.d=pmhahn.de header.i=@pmhahn.de header.b=hp82dTcs reason="signature verification failed"; arc=none smtp.client-ip=88.198.22.186 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=pmhahn.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pmhahn.de Authentication-Results: smtp.subspace.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=pmhahn.de header.i=@pmhahn.de header.b="hp82dTcs" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pmhahn.de; s=202501; t=1779890492; bh=fqnybA+AhkDSoSNFV2pJQ4jb2qbNqk+p3TKkA5krk7E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hp82dTcsVLKnPKstgfVWdlVIYVOPYxRaYY1SYJvB1goNLjklQePdkE2DJKJmG+KuS ZN5GFvT/eQ29OxoX5qFJW6c0VphvVSj8OW+2wGvEhw+s5uGulNEo0hZqC7A+eCiXHF bppHYzbMjvZIbOv2/LPSr2t7gnkdMYy6nnL59XhqzI2FaMr0NRtRVsr7zISkPBM730 +/QLoJ8pHCTb692VdrzD3PLzagVOYbMFwkmkb+kh70zDvqzefDIpWzg6FWEbWVBugJ 4SqWLxMRVqifVaFN2Ns8HgxogJwtnc87Mf8hty39O6hyopggtzb5CiRK/WZnLD8V4n XnVejxB9G2f3Q== Received: from birdy.pmhahn.de (p200300e27741c70018b982d1b498410b.dip0.t-ipconnect.de [IPv6:2003:e2:7741:c700:18b9:82d1:b498:410b]) by birdy.pmhahn.de (Postfix) with ESMTPSA id 7A3762215801; Wed, 27 May 2026 16:01:32 +0200 (CEST) Date: Wed, 27 May 2026 16:01:31 +0200 From: Philipp Matthias Hahn To: Alexander Viro , Christian Brauner , Jan Kara Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: Proper error-handling of cdev_add() after cdev_alloc() ? Message-ID: Mail-Followup-To: Alexander Viro , Christian Brauner , Jan Kara , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Hello, > How should errors of `cdev_add()` after `cdev_alloc()` be handled? sorry for ping-ing you directly, but so far got no answer and I would like to get a definitive answer on this before I spend more time on this to create and send patches. Thank you. Am Tue, May 12, 2026 at 10:20:13AM +0200 schrieb Philipp Matthias Hahn: > The basic schema seems to be like this: > > cdev = cdev_alloc(); > if (!cdev) > return -ENOMEM; > ... > ret = cdev_add(cdev, ...); > if (ret < 0) { > /* WHAT HERE ??? */ > return ret; > } > ... > return 0; // success > > I found 5 case of how errors are handled: > > 1. kfree(cdev); > drivers/media/v4l2-core/v4l2-dev.c:1060 > > 2. kobject_put(&cdev->kobj); > drivers/char/xillybus/xillybus_class.c:107 > fs/char_dev.c:293 > drivers/s390/char/vmlogrdr.c:780 > drivers/tty/tty_io.c:3171 > drivers/uio/uio.c:925 > > 3. cdev_del(cdev); > drivers/char/virtio_console.c:1435 > fs/fuse/cuse.c:419 > drivers/misc/mei/main.c:1318 > drivers/s390/char/tape_class.c:92 > drivers/s390/char/vmur.c:928 > drivers/scsi/sg.c:1560 > drivers/scsi/st.c:4307 > drivers/staging/vme_user/vme_user.c:694 > > 4. No error handling at all. > arch/sh/boards/mach-landisk/gio.c:145 > > 5. panic() > > Currently I'm unsure of what's the correct way. > My current understanding is, that `cdev_del()` should only be called if > `cdev_add()` succeeded, so those findings above should be fixed. But > to what? I guess __register_chrdev() from fs/char_dev.c:293 is correct and kobject_put(&cdev->kobj); should be used. Thank you in advance Philipp