From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751830AbdI2ANA (ORCPT ); Thu, 28 Sep 2017 20:13:00 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:49252 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751219AbdI2AM5 (ORCPT ); Thu, 28 Sep 2017 20:12:57 -0400 Subject: Re: [RFC PATCH 3/3] fs: detect that the i_rwsem has already been taken exclusively From: Mimi Zohar To: Linus Torvalds , Dave Chinner Cc: LSM List , linux-fsdevel , linux-integrity@vger.kernel.org, Christoph Hellwig , Linux Kernel Mailing List , Jan Kara , "Theodore Ts'o" Date: Thu, 28 Sep 2017 20:12:47 -0400 In-Reply-To: References: <1506602373-4799-1-git-send-email-zohar@linux.vnet.ibm.com> <1506602373-4799-4-git-send-email-zohar@linux.vnet.ibm.com> <20170928220215.GC15067@dastard> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.5 (3.20.5-1.fc24) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-MML: disable x-cbid: 17092900-0004-0000-0000-0000022FF794 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17092900-0005-0000-0000-00005E19ABCC Message-Id: <1506643967.5691.46.camel@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-28_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=2 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1709290000 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2017-09-28 at 16:39 -0700, Linus Torvalds wrote: > On Thu, Sep 28, 2017 at 3:02 PM, Dave Chinner wrote: > > On Thu, Sep 28, 2017 at 08:39:33AM -0400, Mimi Zohar wrote: > >> Don't attempt to take the i_rwsem, if it has already been taken > >> exclusively. > >> > >> Signed-off-by: Mimi Zohar > > > > That's bloody awful. > > > > The locking in filesystem IO paths is already complex enough without > > adding a new IO path semantic that says "caller has already locked > > the i_rwsem in some order and some dependencies that we have no idea > > about". > > I do have to admit that I never got a satisfactory answer on why IMA > doesn't just use its own private per-inode lock for this all. > > It isn't using the i_rwsem for file consistency reasons anyway, so it > seems to be purely about serializing the actual signature generation > with the xattr writing, but since IMA does those both, why isn't IMA > just using its own lock (not the filesystem lock) to do that? Originally IMA did define it's own lock, prior to IMA-appraisal.  IMA- appraisal introduced writing the file hash as an xattr, which required taking the i_mutex.  process_measurement() and ima_file_free() took the iint->mutex first and then the i_mutex, while setxattr, chmod and chown took the locks in reverse order.  To resolve the potential deadlock, the iint->mutex was eliminated. Mimi