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Mon, 24 Jun 2019 20:04:41 -0700 Date: Mon, 24 Jun 2019 20:04:39 -0700 From: "Darrick J. Wong" To: Jan Kara Message-ID: <20190625030439.GA5379@magnolia> References: <156116141046.1664939.11424021489724835645.stgit@magnolia> <156116142734.1664939.5074567130774423066.stgit@magnolia> <20190624113737.GG32376@quack2.suse.cz> <20190624215817.GE1611011@magnolia> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190624215817.GE1611011@magnolia> User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9298 signatures=668687 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906250023 X-Headers-End: 1hfbmT-008oJ1-7k Subject: Re: [f2fs-dev] [Ocfs2-devel] [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-efi@vger.kernel.org, linux-mm@kvack.org, clm@fb.com, adilger.kernel@dilger.ca, ocfs2-devel@oss.oracle.com, matthew.garrett@nebula.com, linux-nilfs@vger.kernel.org, linux-ext4@vger.kernel.org, devel@lists.orangefs.org, josef@toxicpanda.com, reiserfs-devel@vger.kernel.org, viro@zeniv.linux.org.uk, dsterba@suse.com, jaegeuk@kernel.org, tytso@mit.edu, ard.biesheuvel@linaro.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, jk@ozlabs.org, jack@suse.com, linux-fsdevel@vger.kernel.org, linux-mtd@lists.infradead.org, linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Mon, Jun 24, 2019 at 02:58:17PM -0700, Darrick J. Wong wrote: > On Mon, Jun 24, 2019 at 01:37:37PM +0200, Jan Kara wrote: > > On Fri 21-06-19 16:57:07, Darrick J. Wong wrote: > > > From: Darrick J. Wong > > > > > > When we're using FS_IOC_SETFLAGS to set the immutable flag on a file, we > > > need to ensure that userspace can't continue to write the file after the > > > file becomes immutable. To make that happen, we have to flush all the > > > dirty pagecache pages to disk to ensure that we can fail a page fault on > > > a mmap'd region, wait for pending directio to complete, and hope the > > > caller locked out any new writes by holding the inode lock. > > > > > > Signed-off-by: Darrick J. Wong > > > > Seeing the way this worked out, is there a reason to have separate > > vfs_ioc_setflags_flush_data() instead of folding the functionality in > > vfs_ioc_setflags_check() (possibly renaming it to > > vfs_ioc_setflags_prepare() to indicate it does already some changes)? I > > don't see any place that would need these two separated... > > XFS needs them to be separated. > > If we even /think/ that we're going to be setting the immutable flag > then we need to grab the IOLOCK and the MMAPLOCK to prevent further > writes while we drain all the directio writes and dirty data. IO > completions for the write draining can take the ILOCK, which means that > we can't have grabbed it yet. > > Next, we grab the ILOCK so we can check the new flags against the inode > and then update the inode core. > > For most filesystems I think it suffices to inode_lock and then do both, > though. Heh, lol, that applies to fssetxattr, not to setflags, because xfs setflags implementation open-codes the relevant fssetxattr pieces. So for setflags we can combine both parts into a single _prepare function. --D > > > +/* > > > + * Flush all pending IO and dirty mappings before setting S_IMMUTABLE on an > > > + * inode via FS_IOC_SETFLAGS. If the flush fails we'll clear the flag before > > > + * returning error. > > > + * > > > + * Note: the caller should be holding i_mutex, or else be sure that > > > + * they have exclusive access to the inode structure. > > > + */ > > > +static inline int vfs_ioc_setflags_flush_data(struct inode *inode, int flags) > > > +{ > > > + int ret; > > > + > > > + if (!vfs_ioc_setflags_need_flush(inode, flags)) > > > + return 0; > > > + > > > + inode_set_flags(inode, S_IMMUTABLE, S_IMMUTABLE); > > > + ret = inode_flush_data(inode); > > > + if (ret) > > > + inode_set_flags(inode, 0, S_IMMUTABLE); > > > + return ret; > > > +} > > > > Also this sets S_IMMUTABLE whenever vfs_ioc_setflags_need_flush() returns > > true. That is currently the right thing but seems like a landmine waiting > > to trip? So I'd just drop the vfs_ioc_setflags_need_flush() abstraction to > > make it clear what's going on. > > Ok. > > --D > > > > > Honza > > -- > > Jan Kara > > SUSE Labs, CR > > _______________________________________________ > Ocfs2-devel mailing list > Ocfs2-devel@oss.oracle.com > https://oss.oracle.com/mailman/listinfo/ocfs2-devel _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel