From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8FF4914A08E; Thu, 5 Sep 2024 09:49:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725529764; cv=none; b=phTkX/YMJD3u9P5524QsM782vrvRIh9RyP2ff46dSzxt2h6rCka/VDzfyLq55lVqZF+7pMtW8tPTC6BzUae+vtNCly7ETZZGsUjK51NYnTVGRBvUr7HxutQrS4yt00EMgK9XlE8ZGg+F+e9WUZAus0MFa/GM3o/SMtxapCpS/pI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725529764; c=relaxed/simple; bh=puLLS8VqHBNYAisw5Plz/y7rjdwYXoq2bS3OJBJV1yA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=n8mMLQBCWpJCPbKhrc6mz6117fP8xkZgo9WoCfKL3vjO7mavo5Txr++dRc7jj89Mme3Qi8oJWyPB7agD40+b0Dra33dM42mbQpdzxQVINne3/eMnECWErxrwtRvsaVxA8bK7lmO5+HuYutG07kWM9QAH6zBYQhDutYDeDO3aMWM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=bVkUmKp3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="bVkUmKp3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13260C4CEC3; Thu, 5 Sep 2024 09:49:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1725529764; bh=puLLS8VqHBNYAisw5Plz/y7rjdwYXoq2bS3OJBJV1yA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bVkUmKp3yAM8Y6btpV7y4zj7nyVieCme9RHBfIDPuGi1SbUNikQnlk7ferpJuFzAX dHdBLT8F6WuVuXEkMQAVsTcNGijMmOSOEWCgnEJH8O+mDGPRLeeLSeXKIU8si+dx6M UQzNAPFnPRyVwQvZewqs2B44quFNpXtN1DXwpYLQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jan Kara , Amir Goldstein , Stephen Brennan , Sasha Levin Subject: [PATCH 6.10 136/184] fsnotify: clear PARENT_WATCHED flags lazily Date: Thu, 5 Sep 2024 11:40:49 +0200 Message-ID: <20240905093737.529330966@linuxfoundation.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240905093732.239411633@linuxfoundation.org> References: <20240905093732.239411633@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Amir Goldstein [ Upstream commit 172e422ffea20a89bfdc672741c1aad6fbb5044e ] In some setups directories can have many (usually negative) dentries. Hence __fsnotify_update_child_dentry_flags() function can take a significant amount of time. Since the bulk of this function happens under inode->i_lock this causes a significant contention on the lock when we remove the watch from the directory as the __fsnotify_update_child_dentry_flags() call from fsnotify_recalc_mask() races with __fsnotify_update_child_dentry_flags() calls from __fsnotify_parent() happening on children. This can lead upto softlockup reports reported by users. Fix the problem by calling fsnotify_update_children_dentry_flags() to set PARENT_WATCHED flags only when parent starts watching children. When parent stops watching children, clear false positive PARENT_WATCHED flags lazily in __fsnotify_parent() for each accessed child. Suggested-by: Jan Kara Signed-off-by: Amir Goldstein Signed-off-by: Stephen Brennan Signed-off-by: Jan Kara Signed-off-by: Sasha Levin --- fs/notify/fsnotify.c | 31 +++++++++++++++++++++---------- fs/notify/fsnotify.h | 2 +- fs/notify/mark.c | 32 +++++++++++++++++++++++++++++--- include/linux/fsnotify_backend.h | 8 +++++--- 4 files changed, 56 insertions(+), 17 deletions(-) diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c index ff69ae24c4e8..272c8a1dab3c 100644 --- a/fs/notify/fsnotify.c +++ b/fs/notify/fsnotify.c @@ -117,17 +117,13 @@ void fsnotify_sb_free(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) +void fsnotify_set_children_dentry_flags(struct inode *inode) { struct dentry *alias; - int watched; if (!S_ISDIR(inode->i_mode)) return; - /* determine if the children should tell inode about their events */ - watched = fsnotify_inode_watches_children(inode); - spin_lock(&inode->i_lock); /* run all of the dentries associated with this inode. Since this is a * directory, there damn well better only be one item on this list */ @@ -143,10 +139,7 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode) continue; spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED); - if (watched) - child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED; - else - child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED; + child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED; spin_unlock(&child->d_lock); } spin_unlock(&alias->d_lock); @@ -154,6 +147,24 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode) spin_unlock(&inode->i_lock); } +/* + * Lazily clear false positive PARENT_WATCHED flag for child whose parent had + * stopped watching children. + */ +static void fsnotify_clear_child_dentry_flag(struct inode *pinode, + struct dentry *dentry) +{ + spin_lock(&dentry->d_lock); + /* + * d_lock is a sufficient barrier to prevent observing a non-watched + * parent state from before the fsnotify_set_children_dentry_flags() + * or fsnotify_update_flags() call that had set PARENT_WATCHED. + */ + if (!fsnotify_inode_watches_children(pinode)) + 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? */ static bool fsnotify_event_needs_parent(struct inode *inode, __u32 mnt_mask, __u32 mask) @@ -228,7 +239,7 @@ 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_clear_child_dentry_flag(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 2d059f789ee3..663759ed6fbc 100644 --- a/fs/notify/fsnotify.h +++ b/fs/notify/fsnotify.h @@ -93,7 +93,7 @@ static inline void fsnotify_clear_marks_by_sb(struct super_block *sb) * 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 void fsnotify_set_children_dentry_flags(struct inode *inode); extern struct kmem_cache *fsnotify_mark_connector_cachep; diff --git a/fs/notify/mark.c b/fs/notify/mark.c index c3eefa70633c..5e170e713088 100644 --- a/fs/notify/mark.c +++ b/fs/notify/mark.c @@ -250,6 +250,24 @@ static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) return fsnotify_update_iref(conn, want_iref); } +static bool fsnotify_conn_watches_children( + struct fsnotify_mark_connector *conn) +{ + if (conn->type != FSNOTIFY_OBJ_TYPE_INODE) + return false; + + return fsnotify_inode_watches_children(fsnotify_conn_inode(conn)); +} + +static void fsnotify_conn_set_children_dentry_flags( + struct fsnotify_mark_connector *conn) +{ + if (conn->type != FSNOTIFY_OBJ_TYPE_INODE) + return; + + fsnotify_set_children_dentry_flags(fsnotify_conn_inode(conn)); +} + /* * Calculate mask of events for a list of marks. The caller must make sure * connector and connector->obj cannot disappear under us. Callers achieve @@ -258,15 +276,23 @@ static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) */ void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) { + bool update_children; + if (!conn) return; spin_lock(&conn->lock); + update_children = !fsnotify_conn_watches_children(conn); __fsnotify_recalc_mask(conn); + update_children &= fsnotify_conn_watches_children(conn); spin_unlock(&conn->lock); - if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) - __fsnotify_update_child_dentry_flags( - fsnotify_conn_inode(conn)); + /* + * Set children's PARENT_WATCHED flags only if parent started watching. + * When parent stops watching, we clear false positive PARENT_WATCHED + * flags lazily in __fsnotify_parent(). + */ + if (update_children) + fsnotify_conn_set_children_dentry_flags(conn); } /* Free all connectors queued for freeing once SRCU period ends */ diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h index 4dd6143db271..8be029bc50b1 100644 --- a/include/linux/fsnotify_backend.h +++ b/include/linux/fsnotify_backend.h @@ -594,12 +594,14 @@ static inline __u32 fsnotify_parent_needed_mask(__u32 mask) static inline int fsnotify_inode_watches_children(struct inode *inode) { + __u32 parent_mask = READ_ONCE(inode->i_fsnotify_mask); + /* FS_EVENT_ON_CHILD is set if the inode may care */ - if (!(inode->i_fsnotify_mask & FS_EVENT_ON_CHILD)) + if (!(parent_mask & FS_EVENT_ON_CHILD)) return 0; /* this inode might care about child events, does it care about the * specific set of events that can happen on a child? */ - return inode->i_fsnotify_mask & FS_EVENTS_POSS_ON_CHILD; + return parent_mask & FS_EVENTS_POSS_ON_CHILD; } /* @@ -613,7 +615,7 @@ static inline void fsnotify_update_flags(struct dentry *dentry) /* * Serialisation of setting PARENT_WATCHED on the dentries is provided * by d_lock. If inotify_inode_watched changes after we have taken - * d_lock, the following __fsnotify_update_child_dentry_flags call will + * d_lock, the following fsnotify_set_children_dentry_flags call will * find our entry, so it will spin until we complete here, and update * us with the new state. */ -- 2.43.0