fsnotify: lazy attach fsnotify_sb_info state to sb

Define a container struct fsnotify_sb_info to hold per-sb state,
including the reference to sb marks connector.

Allocate the fsnotify_sb_info state before attaching connector to any
object on the sb and free it only when killing sb.

This state is going to be used for storing per priority watched objects
counters.

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20240317184154.1200192-8-amir73il@gmail.com>

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 503e7c75e777f9f7bbe2ecb15aae9499c3519811..fb3f36bc6ea9e43ef12263caaaadd79c39b36135 100644 (file)
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -89,11 +89,18 @@ static void fsnotify_unmount_inodes(struct super_block *sb)
 
 void fsnotify_sb_delete(struct super_block *sb)
 {
+       struct fsnotify_sb_info *sbinfo = fsnotify_sb_info(sb);
+
+       /* Were any marks ever added to any object on this sb? */
+       if (!sbinfo)
+               return;
+
        fsnotify_unmount_inodes(sb);
        fsnotify_clear_marks_by_sb(sb);
        /* Wait for outstanding object references from connectors */
        wait_var_event(fsnotify_sb_watched_objects(sb),
                       !atomic_long_read(fsnotify_sb_watched_objects(sb)));
+       kfree(sbinfo);
 }
 
 /*
@@ -489,6 +496,7 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 {
        const struct path *path = fsnotify_data_path(data, data_type);
        struct super_block *sb = fsnotify_data_sb(data, data_type);
+       struct fsnotify_sb_info *sbinfo = fsnotify_sb_info(sb);
        struct fsnotify_iter_info iter_info = {};
        struct mount *mnt = NULL;
        struct inode *inode2 = NULL;
@@ -525,7 +533,7 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
         * SRCU because we have no references to any objects and do not
         * need SRCU to keep them "alive".
         */
-       if (!sb->s_fsnotify_marks &&
+       if ((!sbinfo || !sbinfo->sb_marks) &&
            (!mnt || !mnt->mnt_fsnotify_marks) &&
            (!inode || !inode->i_fsnotify_marks) &&
            (!inode2 || !inode2->i_fsnotify_marks))
@@ -552,8 +560,10 @@ int fsnotify(__u32 mask, const void *data, int data_type, struct inode *dir,
 
        iter_info.srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
 
-       iter_info.marks[FSNOTIFY_ITER_TYPE_SB] =
-               fsnotify_first_mark(&sb->s_fsnotify_marks);
+       if (sbinfo) {
+               iter_info.marks[FSNOTIFY_ITER_TYPE_SB] =
+                       fsnotify_first_mark(&sbinfo->sb_marks);
+       }
        if (mnt) {
                iter_info.marks[FSNOTIFY_ITER_TYPE_VFSMOUNT] =
                        fsnotify_first_mark(&mnt->mnt_fsnotify_marks);

diff --git a/fs/notify/fsnotify.h b/fs/notify/fsnotify.h
index b1fec7cd8ee405b6cd042a5d43200620a6c487ac..2d059f789ee355c7441beefb8872eacffee2f556 100644 (file)
--- a/fs/notify/fsnotify.h
+++ b/fs/notify/fsnotify.h
@@ -54,6 +54,13 @@ static inline struct super_block *fsnotify_connector_sb(
        return fsnotify_object_sb(conn->obj, conn->type);
 }
 
+static inline fsnotify_connp_t *fsnotify_sb_marks(struct super_block *sb)
+{
+       struct fsnotify_sb_info *sbinfo = fsnotify_sb_info(sb);
+
+       return sbinfo ? &sbinfo->sb_marks : NULL;
+}
+
 /* destroy all events sitting in this groups notification queue */
 extern void fsnotify_flush_notify(struct fsnotify_group *group);
 
@@ -79,7 +86,7 @@ static inline void fsnotify_clear_marks_by_mount(struct vfsmount *mnt)
 /* run the list of all marks associated with sb and destroy them */
 static inline void fsnotify_clear_marks_by_sb(struct super_block *sb)
 {
-       fsnotify_destroy_marks(&sb->s_fsnotify_marks);
+       fsnotify_destroy_marks(fsnotify_sb_marks(sb));
 }
 
 /*

diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 647c49c2046739d988672da3068538b5b220aa6b..b2f5d8c9cce11546be7e008b9ffba206ae28821f 100644 (file)
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -106,7 +106,7 @@ static fsnotify_connp_t *fsnotify_object_connp(void *obj,
        case FSNOTIFY_OBJ_TYPE_VFSMOUNT:
                return &real_mount(obj)->mnt_fsnotify_marks;
        case FSNOTIFY_OBJ_TYPE_SB:
-               return &((struct super_block *)obj)->s_fsnotify_marks;
+               return fsnotify_sb_marks(obj);
        default:
                return NULL;
        }
@@ -569,6 +569,26 @@ int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
        return -1;
 }
 
+static int fsnotify_attach_info_to_sb(struct super_block *sb)
+{
+       struct fsnotify_sb_info *sbinfo;
+
+       /* sb info is freed on fsnotify_sb_delete() */
+       sbinfo = kzalloc(sizeof(*sbinfo), GFP_KERNEL);
+       if (!sbinfo)
+               return -ENOMEM;
+
+       /*
+        * cmpxchg() provides the barrier so that callers of fsnotify_sb_info()
+        * will observe an initialized structure
+        */
+       if (cmpxchg(&sb->s_fsnotify_info, NULL, sbinfo)) {
+               /* Someone else created sbinfo for us */
+               kfree(sbinfo);
+       }
+       return 0;
+}
+
 static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
                                               void *obj, unsigned int obj_type)
 {
@@ -640,6 +660,16 @@ static int fsnotify_add_mark_list(struct fsnotify_mark *mark, void *obj,
        if (WARN_ON(!fsnotify_valid_obj_type(obj_type)))
                return -EINVAL;
 
+       /*
+        * Attach the sb info before attaching a connector to any object on sb.
+        * The sb info will remain attached as long as sb lives.
+        */
+       if (!fsnotify_sb_info(sb)) {
+               err = fsnotify_attach_info_to_sb(sb);
+               if (err)
+                       return err;
+       }
+
        connp = fsnotify_object_connp(obj, obj_type);
 restart:
        spin_lock(&mark->lock);

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 00fc429b0af0fb9bbab2382a9e347fdbac383981..7f40b592f7119459da1656dd4d495b310b7d0cfd 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -73,6 +73,8 @@ struct fscrypt_inode_info;
 struct fscrypt_operations;
 struct fsverity_info;
 struct fsverity_operations;
+struct fsnotify_mark_connector;
+struct fsnotify_sb_info;
 struct fs_context;
 struct fs_parameter_spec;
 struct fileattr;
@@ -620,8 +622,6 @@ is_uncached_acl(struct posix_acl *acl)
 #define IOP_XATTR      0x0008
 #define IOP_DEFAULT_READLINK   0x0010
 
-struct fsnotify_mark_connector;
-
 /*
  * Keep mostly read-only and often accessed (especially for
  * the RCU path lookup and 'stat' data) fields at the beginning
@@ -1249,7 +1249,7 @@ struct super_block {
 
        /*
         * Keep s_fs_info, s_time_gran, s_fsnotify_mask, and
-        * s_fsnotify_marks together for cache efficiency. They are frequently
+        * s_fsnotify_info together for cache efficiency. They are frequently
         * accessed and rarely modified.
         */
        void                    *s_fs_info;     /* Filesystem private info */
@@ -1261,7 +1261,7 @@ struct super_block {
        time64_t                   s_time_max;
 #ifdef CONFIG_FSNOTIFY
        __u32                   s_fsnotify_mask;
-       struct fsnotify_mark_connector __rcu    *s_fsnotify_marks;
+       struct fsnotify_sb_info *s_fsnotify_info;
 #endif
 
        /*

diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 83004d9e07a31289b286cc2ba37656c2439c193d..c9f2b2f6b49383064f375b0d84234aeb3c23e0ad 100644 (file)
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -477,6 +477,23 @@ struct fsnotify_mark_connector {
        struct hlist_head list;
 };
 
+/*
+ * Container for per-sb fsnotify state (sb marks and more).
+ * Attached lazily on first marked object on the sb and freed when killing sb.
+ */
+struct fsnotify_sb_info {
+       struct fsnotify_mark_connector __rcu *sb_marks;
+};
+
+static inline struct fsnotify_sb_info *fsnotify_sb_info(struct super_block *sb)
+{
+#ifdef CONFIG_FSNOTIFY
+       return READ_ONCE(sb->s_fsnotify_info);
+#else
+       return NULL;
+#endif
+}
+
 static inline atomic_long_t *fsnotify_sb_watched_objects(struct super_block *sb)
 {
        return &sb->s_fsnotify_connectors;