From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 79822C432BE for ; Wed, 25 Aug 2021 18:40:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4534E6109E for ; Wed, 25 Aug 2021 18:40:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235599AbhHYSlH (ORCPT ); Wed, 25 Aug 2021 14:41:07 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:54222 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232017AbhHYSlH (ORCPT ); Wed, 25 Aug 2021 14:41:07 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: krisman) with ESMTPSA id 7F6401F43C0C From: Gabriel Krisman Bertazi To: Amir Goldstein Cc: Jan Kara , Linux API , Ext4 , linux-fsdevel , Khazhismel Kumykov , David Howells , Dave Chinner , Theodore Tso , "Darrick J. Wong" , Matthew Bobrowski , kernel@collabora.com Subject: Re: [PATCH v6 09/21] fsnotify: Allow events reported with an empty inode Organization: Collabora References: <20210812214010.3197279-1-krisman@collabora.com> <20210812214010.3197279-10-krisman@collabora.com> Date: Wed, 25 Aug 2021 14:40:16 -0400 In-Reply-To: (Amir Goldstein's message of "Fri, 13 Aug 2021 10:58:56 +0300") Message-ID: <87tujdz7u7.fsf@collabora.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org Amir Goldstein writes: > On Fri, Aug 13, 2021 at 12:41 AM Gabriel Krisman Bertazi > wrote: >> >> Some file system events (i.e. FS_ERROR) might not be associated with an >> inode. For these, it makes sense to associate them directly with the >> super block of the file system they apply to. This patch allows the >> event to be reported with a NULL inode, by recovering the superblock >> directly from the data field, if needed. >> >> Signed-off-by: Gabriel Krisman Bertazi >> >> -- >> Changes since v5: >> - add fsnotify_data_sb handle to retrieve sb from the data field. (jan) >> --- >> fs/notify/fsnotify.c | 16 +++++++++++++--- >> 1 file changed, 13 insertions(+), 3 deletions(-) >> >> diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c >> index 30d422b8c0fc..536db02cb26e 100644 >> --- a/fs/notify/fsnotify.c >> +++ b/fs/notify/fsnotify.c >> @@ -98,6 +98,14 @@ void fsnotify_sb_delete(struct super_block *sb) >> fsnotify_clear_marks_by_sb(sb); >> } >> >> +static struct super_block *fsnotify_data_sb(const void *data, int data_type) >> +{ >> + struct inode *inode = fsnotify_data_inode(data, data_type); >> + struct super_block *sb = inode ? inode->i_sb : NULL; >> + >> + return sb; >> +} >> + >> /* >> * Given an inode, first check if we care what happens to our children. Inotify >> * and dnotify both tell their parents about events. If we care about any event >> @@ -455,8 +463,10 @@ static void fsnotify_iter_next(struct fsnotify_iter_info *iter_info) >> * @file_name is relative to >> * @file_name: optional file name associated with event >> * @inode: optional inode associated with event - >> - * either @dir or @inode must be non-NULL. >> - * if both are non-NULL event may be reported to both. >> + * If @dir and @inode are NULL, @data must have a type that >> + * allows retrieving the file system associated with this > > Irrelevant comment. sb must always be available from @data. > >> + * event. if both are non-NULL event may be reported to >> + * both. >> * @cookie: inotify rename cookie >> */ >> int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir, >> @@ -483,7 +493,7 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir, >> */ >> parent = dir; >> } >> - sb = inode->i_sb; >> + sb = inode ? inode->i_sb : fsnotify_data_sb(data, data_type); > > const struct path *path = fsnotify_data_path(data, data_type); > + const struct super_block *sb = fsnotify_data_sb(data, data_type); > > All the games with @data @inode and @dir args are irrelevant to this. > sb should always be available from @data and it does not matter > if fsnotify_data_inode() is the same as @inode, @dir or neither. > All those inodes are anyway on the same sb. Hi Amir, I think this is actually necessary. I could identify at least one event (FS_CREATE | FS_ISDIR) where fsnotify is invoked with a NULL data field. In that case, fsnotify_dirent is called with a negative dentry from vfs_mkdir(). I'm not sure why exactly the dentry is negative after the mkdir, but it would be possible we are racing with the file removal, I guess? It might be a bug in fsnotify that this case even happen, but I'm not sure yet. The easiest way around it is what I proposed: just use inode->i_sb if data is NULL. Since, as you said, data, inode and dir are all on the same superblock, it should work, I think. -- Gabriel Krisman Bertazi