From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Darrick J. Wong" Subject: Re: [Ocfs2-devel] [PATCH 2/7] vfs: flush and wait for io when setting the immutable flag via SETFLAGS Date: Mon, 24 Jun 2019 20:04:39 -0700 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=F3Bn3lgvu1plPP+/sWzVQdJWqxatl+U6p2zq7JMCk28=; b=IKbjv/TfDOsG9F dTNsPgyPNh646s8vorItTR/AkO4/hlqV8ecwKQjLq7nuum04HkcxdJ0+LrMNwpVWk0W7pG7bIgdV/ MyJ9kek/qW0tubLKULP8yBB7I6srjabIJ7fadOaDA4y6McNot/YIwsIj541vMRj42zz8Bv1WxEZzD oWzLm7t2a9g+dZaWe8oyqmhLFw6S83XROdztZqK46tKfK4lBLVvHY99kfI+GY2/5id/quKkYQuYHX rfB4SzJqwZP5nnr1x+gqlcanZSlVBaK3A5PPjhczIpKn7fkBYZaCbokscfWX1cSIU3PiRPCaQyGqf Fi6q723zou0iOP/5Cfcg==; DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2018-07-02; bh=y1nTqvm5zm2oVuuxHsrGpbU4gEqHpmqSXspC8Bne9NM=; b=BXJlUqAKvMETApXDcsKgEZiNdrmlXkQGnY88kMW3AMxNKcXyyaE6UXAlpYECy+ntv7pH 6uhEP1tj4tycY9LMVwQSwCJ1OFoN8XiURaWWP5MgMDhRGeWBYKJ5F+hDMXeWyXvzw09Y W93kGqDhXdEUxHJGprg0ZqzGMSQuXc6a6uPIBselde0/QnSPFrNudLSF4JrDCRjZHlSe PtPwNFzZ3qhrAqfZeA252/OTt3UOJ6W5XclgLFaB43nqCHJq7hk5QCcLKtksxGRz16et vcWpg2Ca0sMBi64yleW6uVf2BPJY2qw2eabFh6Nu+9cNmwvp3CwrP4l2harCRSOmeEeb 1g== Content-Disposition: inline In-Reply-To: <20190624215817.GE1611011@magnolia> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-mtd" Errors-To: linux-mtd-bounces+gldm-linux-mtd-36=gmane.org@lists.infradead.org To: Jan Kara Cc: linux-efi@vger.kernel.org, yuchao0@huawei.com, 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 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 MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/