On Wed, Mar 20, 2024 at 10:47 AM Christian Brauner <brauner@xxxxxxxxxx> wrote:
>
> On Sun, Mar 17, 2024 at 08:41:51PM +0200, Amir Goldstein wrote:
> > 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@xxxxxxx>
> > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> > ---
> > fs/notify/fsnotify.c | 16 +++++++++++++---
> > fs/notify/fsnotify.h | 9 ++++++++-
> > fs/notify/mark.c | 32 +++++++++++++++++++++++++++++++-
> > include/linux/fs.h | 8 ++++----
> > include/linux/fsnotify_backend.h | 17 +++++++++++++++++
> > 5 files changed, 73 insertions(+), 9 deletions(-)
> >
> > diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
> > index 503e7c75e777..fb3f36bc6ea9 100644
> > --- 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 8b73ad45cc71..378f9ec6d64b 100644
> > --- a/fs/notify/fsnotify.h
> > +++ b/fs/notify/fsnotify.h
> > @@ -53,6 +53,13 @@ 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);
> >
> > @@ -78,7 +85,7 @@ 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 0b703f9e6344..db053e0e218d 100644
> > --- a/fs/notify/mark.c
> > +++ b/fs/notify/mark.c
> > @@ -105,7 +105,7 @@ static fsnotify_connp_t *fsnotify_object_connp(void *obj, int obj_type)
> > 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;
> > }
> > @@ -568,6 +568,26 @@ 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);
> > + }
>
> Alternatively, you could consider using wait_var_event() to let
> concurrent attachers wait for s_fsnotify_info to be initialized using a
> sentinel value to indicate that the caller should wait. But not sure if
> it's worth it.
Not worth it IMO. Adding watches is an extremely rare event
in the grand picture.
Thanks,
Amir.
