5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Amir Goldstein amir73il@gmail.com
[ 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 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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 7974e91ffe13..b5d8f238fce4 100644 --- a/fs/notify/fsnotify.c +++ b/fs/notify/fsnotify.c @@ -103,17 +103,13 @@ 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) +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 */ @@ -129,10 +125,7 @@ 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); @@ -140,6 +133,24 @@ 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, struct mount *mnt, __u32 mask) @@ -208,7 +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_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 fde74eb333cc..2b4267de86e6 100644 --- a/fs/notify/fsnotify.h +++ b/fs/notify/fsnotify.h @@ -74,7 +74,7 @@ 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 c74ef947447d..4be6e883d492 100644 --- a/fs/notify/mark.c +++ b/fs/notify/mark.c @@ -176,6 +176,24 @@ 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 @@ -184,15 +202,23 @@ 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 d7d96c806bff..096b79e4373f 100644 --- a/include/linux/fsnotify_backend.h +++ b/include/linux/fsnotify_backend.h @@ -563,12 +563,14 @@ 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; }
/* @@ -582,7 +584,7 @@ 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. */