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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E1472C433FE for ; Fri, 21 Oct 2022 09:18:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231166AbiJUJSS (ORCPT ); Fri, 21 Oct 2022 05:18:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43628 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231145AbiJUJSO (ORCPT ); Fri, 21 Oct 2022 05:18:14 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2C232565C1; Fri, 21 Oct 2022 02:18:00 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 16690B82A2D; Fri, 21 Oct 2022 09:17:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1AC3BC433D6; Fri, 21 Oct 2022 09:17:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666343835; bh=nJQIG7eMdgvCQHUqn+x+OTgBKkxaBGtjNSHBvblPK6U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=M8KAatuffLbqLPdmCbdRAEoQmAM4Xwt6l+h9GAluMntgCXEbJz30bl78WqyPI/tZ4 Vl7+tUJ3On77kf2t9u4H20KKjJv6fJA0J84qXikAJIhTOzUWaJOTISk9p+zJUXT3kV CqwWY9B7CPYAUwyXh08tyuq1yEXj1pTgZNvcwL5g/4atWXet5g039IX6nEKnh/Ag2K NPQzYn9oI43FRzXuTbvQvzG4MdlsgAp1frF0Ir1zBwcCDWuOoqX+++WmNV2hryN1bO SOJ1gFaRzZOwy3yVwfTG3u8Ffufs60Us98ZwKjqdOcdI0X850NntPkAgZwcUn+YNIP m0T2PhtSEeiWg== Date: Fri, 21 Oct 2022 11:17:10 +0200 From: Christian Brauner To: Stephen Brennan Cc: Jan Kara , Alexander Viro , linux-fsdevel@vger.kernel.org, Amir Goldstein , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/3] fsnotify: Protect i_fsnotify_mask and child flags with inode rwsem Message-ID: <20221021091710.jxv6zi3nfkmqdmqy@wittgenstein> References: <20221018041233.376977-1-stephen.s.brennan@oracle.com> <20221021010310.29521-1-stephen.s.brennan@oracle.com> <20221021010310.29521-3-stephen.s.brennan@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221021010310.29521-3-stephen.s.brennan@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 20, 2022 at 06:03:09PM -0700, Stephen Brennan wrote: > When an inode is interested in events on its children, it must set > DCACHE_FSNOTIFY_PARENT_WATCHED flag on all its children. Currently, when > the fsnotify connector is removed and i_fsnotify_mask becomes zero, we > lazily allow __fsnotify_parent() to do this the next time we see an > event on a child. > > However, if the list of children is very long (e.g., in the millions), > and lots of activity is occurring on the directory, then it's possible > for many CPUs to end up blocked on the inode spinlock in > __fsnotify_update_child_flags(). Each CPU will then redundantly iterate > over the very long list of children. This situation can cause soft > lockups. > > To avoid this, stop lazily updating child flags in __fsnotify_parent(). > Instead, update flags when we disconnect a mark connector. Remember the > state of the children flags in the fsnotify_mark_connector flags. > Provide mutual exclusion by holding i_rwsem exclusive while we update > children, and use the cached state to avoid updating flags > unnecessarily. > > Signed-off-by: Stephen Brennan > --- > > fs/notify/fsnotify.c | 22 ++++++- > fs/notify/fsnotify.h | 31 ++++++++- > fs/notify/mark.c | 106 ++++++++++++++++++++----------- > include/linux/fsnotify_backend.h | 8 +++ > 4 files changed, 127 insertions(+), 40 deletions(-) > > diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c > index 6c338322f0c3..f83eca4fb841 100644 > --- a/fs/notify/fsnotify.c > +++ b/fs/notify/fsnotify.c > @@ -103,13 +103,15 @@ void fsnotify_sb_delete(struct super_block *sb) > * parent cares. Thus when an event happens on a child it can quickly tell > * if there is a need to find a parent and send the event to the parent. > */ > -void __fsnotify_update_child_dentry_flags(struct inode *inode) > +bool __fsnotify_update_children_dentry_flags(struct inode *inode) > { > struct dentry *alias, *child; > int watched; > > if (!S_ISDIR(inode->i_mode)) > - return; > + return false; > + > + lockdep_assert_held_write(&inode->i_rwsem); > > /* determine if the children should tell inode about their events */ > watched = fsnotify_inode_watches_children(inode); > @@ -133,6 +135,20 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode) > spin_unlock(&child->d_lock); > } > spin_unlock(&alias->d_lock); > + return watched; > +} > + > +void __fsnotify_update_child_dentry_flags(struct inode *inode, struct dentry *dentry) > +{ > + /* > + * Flag would be cleared soon by > + * __fsnotify_update_child_dentry_flags(), but as an > + * optimization, clear it now. > + */ > + spin_lock(&dentry->d_lock); > + if (!fsnotify_inode_watches_children(inode)) > + dentry->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED; > + spin_unlock(&dentry->d_lock); > } > > /* Are inode/sb/mount interested in parent and name info with this event? */ > @@ -203,7 +219,7 @@ int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data, > p_inode = parent->d_inode; > p_mask = fsnotify_inode_watches_children(p_inode); > if (unlikely(parent_watched && !p_mask)) > - __fsnotify_update_child_dentry_flags(p_inode); > + __fsnotify_update_child_dentry_flags(p_inode, dentry); > > /* > * Include parent/name in notification either if some notification > diff --git a/fs/notify/fsnotify.h b/fs/notify/fsnotify.h > index fde74eb333cc..182d93014c6b 100644 > --- a/fs/notify/fsnotify.h > +++ b/fs/notify/fsnotify.h > @@ -70,11 +70,40 @@ static inline void fsnotify_clear_marks_by_sb(struct super_block *sb) > fsnotify_destroy_marks(&sb->s_fsnotify_marks); > } > > +static inline bool fsnotify_children_need_update(struct fsnotify_mark_connector *conn, > + struct inode *inode) > +{ > + bool watched, flags_set; > + watched = fsnotify_inode_watches_children(inode); nit: I'd leave a blank line after the variable declarations. Same for fsnotify_update_children_dentry_flags() below. > + flags_set = conn->flags & FSNOTIFY_CONN_FLAG_WATCHES_CHILDREN; > + return (watched && !flags_set) || (!watched && flags_set); > +} > + > /* > * update the dentry->d_flags of all of inode's children to indicate if inode cares > * about events that happen to its children. > */ > -extern void __fsnotify_update_child_dentry_flags(struct inode *inode); > +extern bool __fsnotify_update_children_dentry_flags(struct inode *inode); > + > +static inline void fsnotify_update_children_dentry_flags(struct fsnotify_mark_connector *conn, > + struct inode *inode) Should that be a static inline function in a header seems a bit big. :)