5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Amir Goldstein <amir73il@xxxxxxxxx> [ Upstream commit c3638b5b13740fa31762d414bbce8b7a694e582a ] fsnotify_add_mark() and variants implicitly take a reference on inode when attaching a mark to an inode. Make that behavior opt-out with the mark flag FSNOTIFY_MARK_FLAG_NO_IREF. Instead of taking the inode reference when attaching connector to inode and dropping the inode reference when detaching connector from inode, take the inode reference on attach of the first mark that wants to hold an inode reference and drop the inode reference on detach of the last mark that wants to hold an inode reference. Backends can "upgrade" an existing mark to take an inode reference, but cannot "downgrade" a mark with inode reference to release the refernce. This leaves the choice to the backend whether or not to pin the inode when adding an inode mark. This is intended to be used when adding a mark with ignored mask that is used for optimization in cases where group can afford getting unneeded events and reinstate the mark with ignored mask when inode is accessed again after being evicted. Link: https://lore.kernel.org/r/20220422120327.3459282-12-amir73il@xxxxxxxxx Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> Signed-off-by: Jan Kara <jack@xxxxxxx> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> --- fs/notify/mark.c | 76 +++++++++++++++++++++++--------- include/linux/fsnotify_backend.h | 2 + 2 files changed, 58 insertions(+), 20 deletions(-) diff --git a/fs/notify/mark.c b/fs/notify/mark.c index 982ca2f20ff5d..c74ef947447d6 100644 --- a/fs/notify/mark.c +++ b/fs/notify/mark.c @@ -116,20 +116,64 @@ __u32 fsnotify_conn_mask(struct fsnotify_mark_connector *conn) return *fsnotify_conn_mask_p(conn); } -static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) +static void fsnotify_get_inode_ref(struct inode *inode) +{ + ihold(inode); + atomic_long_inc(&inode->i_sb->s_fsnotify_connectors); +} + +/* + * Grab or drop inode reference for the connector if needed. + * + * When it's time to drop the reference, we only clear the HAS_IREF flag and + * return the inode object. fsnotify_drop_object() will be resonsible for doing + * iput() outside of spinlocks. This happens when last mark that wanted iref is + * detached. + */ +static struct inode *fsnotify_update_iref(struct fsnotify_mark_connector *conn, + bool want_iref) +{ + bool has_iref = conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF; + struct inode *inode = NULL; + + if (conn->type != FSNOTIFY_OBJ_TYPE_INODE || + want_iref == has_iref) + return NULL; + + if (want_iref) { + /* Pin inode if any mark wants inode refcount held */ + fsnotify_get_inode_ref(fsnotify_conn_inode(conn)); + conn->flags |= FSNOTIFY_CONN_FLAG_HAS_IREF; + } else { + /* Unpin inode after detach of last mark that wanted iref */ + inode = fsnotify_conn_inode(conn); + conn->flags &= ~FSNOTIFY_CONN_FLAG_HAS_IREF; + } + + return inode; +} + +static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) { u32 new_mask = 0; + bool want_iref = false; struct fsnotify_mark *mark; assert_spin_locked(&conn->lock); /* We can get detached connector here when inode is getting unlinked. */ if (!fsnotify_valid_obj_type(conn->type)) - return; + return NULL; hlist_for_each_entry(mark, &conn->list, obj_list) { - if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) - new_mask |= fsnotify_calc_mask(mark); + if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) + continue; + new_mask |= fsnotify_calc_mask(mark); + if (conn->type == FSNOTIFY_OBJ_TYPE_INODE && + !(mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF)) + want_iref = true; } *fsnotify_conn_mask_p(conn) = new_mask; + + return fsnotify_update_iref(conn, want_iref); } /* @@ -169,12 +213,6 @@ static void fsnotify_connector_destroy_workfn(struct work_struct *work) } } -static void fsnotify_get_inode_ref(struct inode *inode) -{ - ihold(inode); - atomic_long_inc(&inode->i_sb->s_fsnotify_connectors); -} - static void fsnotify_put_inode_ref(struct inode *inode) { struct super_block *sb = inode->i_sb; @@ -213,6 +251,10 @@ static void *fsnotify_detach_connector_from_object( if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) { inode = fsnotify_conn_inode(conn); inode->i_fsnotify_mask = 0; + + /* Unpin inode when detaching from connector */ + if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF)) + inode = NULL; } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) { fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0; } else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) { @@ -274,7 +316,8 @@ void fsnotify_put_mark(struct fsnotify_mark *mark) objp = fsnotify_detach_connector_from_object(conn, &type); free_conn = true; } else { - __fsnotify_recalc_mask(conn); + objp = __fsnotify_recalc_mask(conn); + type = conn->type; } WRITE_ONCE(mark->connector, NULL); spin_unlock(&conn->lock); @@ -497,7 +540,6 @@ static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp, unsigned int obj_type, __kernel_fsid_t *fsid) { - struct inode *inode = NULL; struct fsnotify_mark_connector *conn; conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL); @@ -505,6 +547,7 @@ static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp, return -ENOMEM; spin_lock_init(&conn->lock); INIT_HLIST_HEAD(&conn->list); + conn->flags = 0; conn->type = obj_type; conn->obj = connp; /* Cache fsid of filesystem containing the object */ @@ -515,10 +558,6 @@ static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp, conn->fsid.val[0] = conn->fsid.val[1] = 0; conn->flags = 0; } - if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) { - inode = fsnotify_conn_inode(conn); - fsnotify_get_inode_ref(inode); - } fsnotify_get_sb_connectors(conn); /* @@ -527,8 +566,6 @@ static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp, */ if (cmpxchg(connp, NULL, conn)) { /* Someone else created list structure for us */ - if (inode) - fsnotify_put_inode_ref(inode); fsnotify_put_sb_connectors(conn); kmem_cache_free(fsnotify_mark_connector_cachep, conn); } @@ -690,8 +727,7 @@ int fsnotify_add_mark_locked(struct fsnotify_mark *mark, if (ret) goto err; - if (mark->mask || mark->ignored_mask) - fsnotify_recalc_mask(mark->connector); + fsnotify_recalc_mask(mark->connector); return ret; err: diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h index d62111e832440..9a1a9e78f69f5 100644 --- a/include/linux/fsnotify_backend.h +++ b/include/linux/fsnotify_backend.h @@ -456,6 +456,7 @@ struct fsnotify_mark_connector { spinlock_t lock; unsigned short type; /* Type of object [lock] */ #define FSNOTIFY_CONN_FLAG_HAS_FSID 0x01 +#define FSNOTIFY_CONN_FLAG_HAS_IREF 0x02 unsigned short flags; /* flags [lock] */ __kernel_fsid_t fsid; /* fsid of filesystem containing object */ union { @@ -510,6 +511,7 @@ struct fsnotify_mark { #define FSNOTIFY_MARK_FLAG_IN_ONESHOT 0x0020 /* fanotify mark flags */ #define FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY 0x0100 +#define FSNOTIFY_MARK_FLAG_NO_IREF 0x0200 unsigned int flags; /* flags [mark->lock] */ }; -- 2.43.0
