bcachefs: Fix bch2_evict_subvolume_inodes()

This fixes a bug in bch2_evict_subvolume_inodes(): d_mark_dontcache()
doesn't handle the case where i_count is already 0, we need to grab and
put the inode in order for it to be dropped.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs.h

@@ -971,6 +971,10 @@ struct bch_fs {
 	reflink_gc_table	reflink_gc_table;
 	size_t			reflink_gc_nr;
 
+	/* fs.c */
+	struct list_head	vfs_inodes_list;
+	struct mutex		vfs_inodes_lock;
+
 	/* VFS IO PATH - fs-io.c */
 	struct bio_set		writepage_bioset;
 	struct bio_set		dio_write_bioset;

fs/bcachefs/darray.h

@@ -19,11 +19,11 @@ struct {								\
 
 typedef DARRAY(void) darray_void;
 
-static inline int __darray_make_room(darray_void *d, size_t t_size, size_t more)
+static inline int __darray_make_room(darray_void *d, size_t t_size, size_t more, gfp_t gfp)
 {
 	if (d->nr + more > d->size) {
 		size_t new_size = roundup_pow_of_two(d->nr + more);
-		void *data = krealloc_array(d->data, new_size, t_size, GFP_KERNEL);
+		void *data = krealloc_array(d->data, new_size, t_size, gfp);
 
 		if (!data)
 			return -ENOMEM;
@@ -35,20 +35,25 @@ static inline int __darray_make_room(darray_void *d, size_t t_size, size_t more)
 	return 0;
 }
 
+#define darray_make_room_gfp(_d, _more, _gfp)				\
+	__darray_make_room((darray_void *) (_d), sizeof((_d)->data[0]), (_more), _gfp)
+
 #define darray_make_room(_d, _more)					\
-	__darray_make_room((darray_void *) (_d), sizeof((_d)->data[0]), (_more))
+	darray_make_room_gfp(_d, _more, GFP_KERNEL)
 
 #define darray_top(_d)		((_d).data[(_d).nr])
 
-#define darray_push(_d, _item)						\
+#define darray_push_gfp(_d, _item, _gfp)				\
 ({									\
-	int _ret = darray_make_room((_d), 1);				\
+	int _ret = darray_make_room_gfp((_d), 1, _gfp);			\
 									\
 	if (!_ret)							\
 		(_d)->data[(_d)->nr++] = (_item);			\
 	_ret;								\
 })
 
+#define darray_push(_d, _item)	darray_push_gfp(_d, _item, GFP_KERNEL)
+
 #define darray_insert_item(_d, _pos, _item)				\
 ({									\
 	size_t pos = (_pos);						\

fs/bcachefs/fs.c

@@ -201,6 +201,10 @@ struct inode *bch2_vfs_inode_get(struct bch_fs *c, subvol_inum inum)
 		return ERR_PTR(ret);
 	}
 
+	mutex_lock(&c->vfs_inodes_lock);
+	list_add(&inode->ei_vfs_inode_list, &c->vfs_inodes_list);
+	mutex_unlock(&c->vfs_inodes_lock);
+
 	unlock_new_inode(&inode->v);
 
 	return &inode->v;
@@ -314,6 +318,9 @@ err_before_quota:
 
 		inode = old;
 	} else {
+		mutex_lock(&c->vfs_inodes_lock);
+		list_add(&inode->ei_vfs_inode_list, &c->vfs_inodes_list);
+		mutex_unlock(&c->vfs_inodes_lock);
 		/*
 		 * we really don't want insert_inode_locked2() to be setting
 		 * I_NEW...
@@ -1370,6 +1377,7 @@ static struct inode *bch2_alloc_inode(struct super_block *sb)
 	inode_init_once(&inode->v);
 	mutex_init(&inode->ei_update_lock);
 	two_state_lock_init(&inode->ei_pagecache_lock);
+	INIT_LIST_HEAD(&inode->ei_vfs_inode_list);
 	mutex_init(&inode->ei_quota_lock);
 
 	return &inode->v;
@@ -1434,53 +1442,78 @@ static void bch2_evict_inode(struct inode *vinode)
 				KEY_TYPE_QUOTA_WARN);
 		bch2_inode_rm(c, inode_inum(inode));
 	}
+
+	mutex_lock(&c->vfs_inodes_lock);
+	list_del_init(&inode->ei_vfs_inode_list);
+	mutex_unlock(&c->vfs_inodes_lock);
 }
 
-void bch2_evict_subvolume_inodes(struct bch_fs *c,
-				 snapshot_id_list *s)
+void bch2_evict_subvolume_inodes(struct bch_fs *c, snapshot_id_list *s)
 {
-	struct super_block *sb = c->vfs_sb;
-	struct inode *inode;
+	struct bch_inode_info *inode, **i;
+	DARRAY(struct bch_inode_info *) grabbed;
+	bool clean_pass = false, this_pass_clean;
 
-	spin_lock(&sb->s_inode_list_lock);
-	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
-		if (!snapshot_list_has_id(s, to_bch_ei(inode)->ei_subvol) ||
-		    (inode->i_state & I_FREEING))
-			continue;
+	/*
+	 * Initially, we scan for inodes without I_DONTCACHE, then mark them to
+	 * be pruned with d_mark_dontcache().
+	 *
+	 * Once we've had a clean pass where we didn't find any inodes without
+	 * I_DONTCACHE, we wait for them to be freed:
+	 */
 
-		d_mark_dontcache(inode);
-		d_prune_aliases(inode);
-	}
-	spin_unlock(&sb->s_inode_list_lock);
+	darray_init(&grabbed);
+	darray_make_room(&grabbed, 1024);
 again:
 	cond_resched();
-	spin_lock(&sb->s_inode_list_lock);
-	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
-		if (!snapshot_list_has_id(s, to_bch_ei(inode)->ei_subvol) ||
-		    (inode->i_state & I_FREEING))
+	this_pass_clean = true;
+
+	mutex_lock(&c->vfs_inodes_lock);
+	list_for_each_entry(inode, &c->vfs_inodes_list, ei_vfs_inode_list) {
+		if (!snapshot_list_has_id(s, inode->ei_subvol))
 			continue;
 
-		if (!(inode->i_state & I_DONTCACHE)) {
-			d_mark_dontcache(inode);
-			d_prune_aliases(inode);
-		}
+		if (!(inode->v.i_state & I_DONTCACHE) &&
+		    !(inode->v.i_state & I_FREEING)) {
+			this_pass_clean = false;
+
+			d_mark_dontcache(&inode->v);
+			d_prune_aliases(&inode->v);
+
+			/*
+			 * If i_count was zero, we have to take and release a
+			 * ref in order for I_DONTCACHE to be noticed and the
+			 * inode to be dropped;
+			 */
+
+			if (!atomic_read(&inode->v.i_count) &&
+			    igrab(&inode->v) &&
+			    darray_push_gfp(&grabbed, inode, GFP_ATOMIC|__GFP_NOWARN))
+				break;
+		} else if (clean_pass && this_pass_clean) {
+			wait_queue_head_t *wq = bit_waitqueue(&inode->v.i_state, __I_NEW);
+			DEFINE_WAIT_BIT(wait, &inode->v.i_state, __I_NEW);
 
-		spin_lock(&inode->i_lock);
-		if (snapshot_list_has_id(s, to_bch_ei(inode)->ei_subvol) &&
-		    !(inode->i_state & I_FREEING)) {
-			wait_queue_head_t *wq = bit_waitqueue(&inode->i_state, __I_NEW);
-			DEFINE_WAIT_BIT(wait, &inode->i_state, __I_NEW);
 			prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
-			spin_unlock(&inode->i_lock);
-			spin_unlock(&sb->s_inode_list_lock);
+			mutex_unlock(&c->vfs_inodes_lock);
+
 			schedule();
 			finish_wait(wq, &wait.wq_entry);
 			goto again;
 		}
-
-		spin_unlock(&inode->i_lock);
 	}
-	spin_unlock(&sb->s_inode_list_lock);
+	mutex_unlock(&c->vfs_inodes_lock);
+
+	darray_for_each(grabbed, i)
+		iput(&(*i)->v);
+	grabbed.nr = 0;
+
+	if (!clean_pass || !this_pass_clean) {
+		clean_pass = this_pass_clean;
+		goto again;
+	}
+
+	darray_exit(&grabbed);
 }
 
 static int bch2_statfs(struct dentry *dentry, struct kstatfs *buf)

fs/bcachefs/fs.h

@@ -13,6 +13,7 @@
 
 struct bch_inode_info {
 	struct inode		v;
+	struct list_head	ei_vfs_inode_list;
 	unsigned long		ei_flags;
 
 	struct mutex		ei_update_lock;

fs/bcachefs/inode.c

@@ -803,9 +803,6 @@ retry:
 
 	bch2_inode_unpack(k, &inode_u);
 
-	/* Subvolume root? */
-	BUG_ON(inode_u.bi_subvol);
-
 	bkey_inode_generation_init(&delete.k_i);
 	delete.k.p = iter.pos;
 	delete.v.bi_generation = cpu_to_le32(inode_u.bi_generation + 1);

fs/bcachefs/super.c

@@ -709,6 +709,9 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
 
 	sema_init(&c->io_in_flight, 128);
 
+	INIT_LIST_HEAD(&c->vfs_inodes_list);
+	mutex_init(&c->vfs_inodes_lock);
+
 	c->copy_gc_enabled		= 1;
 	c->rebalance.enabled		= 1;
 	c->promote_whole_extents	= true;