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fsnotify: clear PARENT_WATCHED flags lazily
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 <jack@suse.cz> Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com> Signed-off-by: Jan Kara <jack@suse.cz>
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@ -117,17 +117,13 @@ void fsnotify_sb_free(struct super_block *sb)
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* parent cares. Thus when an event happens on a child it can quickly tell
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* if there is a need to find a parent and send the event to the parent.
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*/
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void __fsnotify_update_child_dentry_flags(struct inode *inode)
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void fsnotify_set_children_dentry_flags(struct inode *inode)
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{
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struct dentry *alias;
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int watched;
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if (!S_ISDIR(inode->i_mode))
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return;
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/* determine if the children should tell inode about their events */
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watched = fsnotify_inode_watches_children(inode);
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spin_lock(&inode->i_lock);
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/* run all of the dentries associated with this inode. Since this is a
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* directory, there damn well better only be one item on this list */
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@ -143,10 +139,7 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
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continue;
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spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
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if (watched)
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child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
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else
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child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
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child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
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spin_unlock(&child->d_lock);
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}
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spin_unlock(&alias->d_lock);
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@ -154,6 +147,24 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
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spin_unlock(&inode->i_lock);
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}
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/*
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* Lazily clear false positive PARENT_WATCHED flag for child whose parent had
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* stopped watching children.
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*/
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static void fsnotify_clear_child_dentry_flag(struct inode *pinode,
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struct dentry *dentry)
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{
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spin_lock(&dentry->d_lock);
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/*
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* d_lock is a sufficient barrier to prevent observing a non-watched
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* parent state from before the fsnotify_set_children_dentry_flags()
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* or fsnotify_update_flags() call that had set PARENT_WATCHED.
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*/
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if (!fsnotify_inode_watches_children(pinode))
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dentry->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
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spin_unlock(&dentry->d_lock);
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}
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/* Are inode/sb/mount interested in parent and name info with this event? */
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static bool fsnotify_event_needs_parent(struct inode *inode, __u32 mnt_mask,
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__u32 mask)
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@ -228,7 +239,7 @@ int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data,
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p_inode = parent->d_inode;
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p_mask = fsnotify_inode_watches_children(p_inode);
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if (unlikely(parent_watched && !p_mask))
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__fsnotify_update_child_dentry_flags(p_inode);
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fsnotify_clear_child_dentry_flag(p_inode, dentry);
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/*
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* Include parent/name in notification either if some notification
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@ -93,7 +93,7 @@ static inline void fsnotify_clear_marks_by_sb(struct super_block *sb)
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* update the dentry->d_flags of all of inode's children to indicate if inode cares
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* about events that happen to its children.
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*/
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extern void __fsnotify_update_child_dentry_flags(struct inode *inode);
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extern void fsnotify_set_children_dentry_flags(struct inode *inode);
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extern struct kmem_cache *fsnotify_mark_connector_cachep;
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@ -250,6 +250,24 @@ static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
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return fsnotify_update_iref(conn, want_iref);
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}
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static bool fsnotify_conn_watches_children(
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struct fsnotify_mark_connector *conn)
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{
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if (conn->type != FSNOTIFY_OBJ_TYPE_INODE)
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return false;
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return fsnotify_inode_watches_children(fsnotify_conn_inode(conn));
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}
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static void fsnotify_conn_set_children_dentry_flags(
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struct fsnotify_mark_connector *conn)
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{
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if (conn->type != FSNOTIFY_OBJ_TYPE_INODE)
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return;
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fsnotify_set_children_dentry_flags(fsnotify_conn_inode(conn));
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}
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/*
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* Calculate mask of events for a list of marks. The caller must make sure
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* connector and connector->obj cannot disappear under us. Callers achieve
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@ -258,15 +276,23 @@ static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
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*/
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void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
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{
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bool update_children;
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if (!conn)
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return;
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spin_lock(&conn->lock);
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update_children = !fsnotify_conn_watches_children(conn);
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__fsnotify_recalc_mask(conn);
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update_children &= fsnotify_conn_watches_children(conn);
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spin_unlock(&conn->lock);
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if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
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__fsnotify_update_child_dentry_flags(
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fsnotify_conn_inode(conn));
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/*
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* Set children's PARENT_WATCHED flags only if parent started watching.
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* When parent stops watching, we clear false positive PARENT_WATCHED
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* flags lazily in __fsnotify_parent().
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*/
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if (update_children)
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fsnotify_conn_set_children_dentry_flags(conn);
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}
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/* Free all connectors queued for freeing once SRCU period ends */
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@ -594,12 +594,14 @@ static inline __u32 fsnotify_parent_needed_mask(__u32 mask)
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static inline int fsnotify_inode_watches_children(struct inode *inode)
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{
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__u32 parent_mask = READ_ONCE(inode->i_fsnotify_mask);
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/* FS_EVENT_ON_CHILD is set if the inode may care */
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if (!(inode->i_fsnotify_mask & FS_EVENT_ON_CHILD))
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if (!(parent_mask & FS_EVENT_ON_CHILD))
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return 0;
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/* this inode might care about child events, does it care about the
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* specific set of events that can happen on a child? */
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return inode->i_fsnotify_mask & FS_EVENTS_POSS_ON_CHILD;
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return parent_mask & FS_EVENTS_POSS_ON_CHILD;
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}
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/*
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@ -613,7 +615,7 @@ static inline void fsnotify_update_flags(struct dentry *dentry)
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/*
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* Serialisation of setting PARENT_WATCHED on the dentries is provided
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* by d_lock. If inotify_inode_watched changes after we have taken
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* d_lock, the following __fsnotify_update_child_dentry_flags call will
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* d_lock, the following fsnotify_set_children_dentry_flags call will
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* find our entry, so it will spin until we complete here, and update
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* us with the new state.
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*/
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