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Commit 2a285686 authored by Kent Overstreet's avatar Kent Overstreet
Browse files

bcache: btree locking rework 



Add a new lock, b->write_lock, which is required to actually modify - or write -
a btree node; this lock is only held for short durations.

This means we can write out a btree node without taking b->lock, which _is_ held
for long durations - solving a deadlock when btree_flush_write() (from the
journalling code) is called with a btree node locked.

Right now just occurs in bch_btree_set_root(), but with an upcoming journalling
rework is going to happen a lot more.

This also turns b->lock is now more of a read/intent lock instead of a
read/write lock - but not completely, since it still blocks readers. May turn it
into a real intent lock at some point in the future.

Signed-off-by: default avatarKent Overstreet <kmo@daterainc.com>
parent 05335cff

drivers/md/bcache/btree.c

+119 −45
Original line number Diff line number Diff line
@@ -167,6 +167,20 @@ static inline struct bset *write_block(struct btree *b) 
	return ((void *) btree_bset_first(b)) + b->written * block_bytes(b->c);

}



static void bch_btree_init_next(struct btree *b)

{

	/* If not a leaf node, always sort */

	if (b->level && b->keys.nsets)

		bch_btree_sort(&b->keys, &b->c->sort);

	else

		bch_btree_sort_lazy(&b->keys, &b->c->sort);



	if (b->written < btree_blocks(b))

		bch_bset_init_next(&b->keys, write_block(b),

				   bset_magic(&b->c->sb));



}



/* Btree key manipulation */



void bkey_put(struct cache_set *c, struct bkey *k)
@@ -438,10 +452,12 @@ static void do_btree_node_write(struct btree *b) 
	}

}



void bch_btree_node_write(struct btree *b, struct closure *parent)

void __bch_btree_node_write(struct btree *b, struct closure *parent)

{

	struct bset *i = btree_bset_last(b);



	lockdep_assert_held(&b->write_lock);



	trace_bcache_btree_write(b);



	BUG_ON(current->bio_list);
@@ -465,23 +481,24 @@ void bch_btree_node_write(struct btree *b, struct closure *parent) 
			&PTR_CACHE(b->c, &b->key, 0)->btree_sectors_written);



	b->written += set_blocks(i, block_bytes(b->c));

}



	/* If not a leaf node, always sort */

	if (b->level && b->keys.nsets)

		bch_btree_sort(&b->keys, &b->c->sort);

	else

		bch_btree_sort_lazy(&b->keys, &b->c->sort);

void bch_btree_node_write(struct btree *b, struct closure *parent)

{

	unsigned nsets = b->keys.nsets;



	lockdep_assert_held(&b->lock);



	__bch_btree_node_write(b, parent);



	/*

	 * do verify if there was more than one set initially (i.e. we did a

	 * sort) and we sorted down to a single set:

	 */

	if (i != b->keys.set->data && !b->keys.nsets)

	if (nsets && !b->keys.nsets)

		bch_btree_verify(b);



	if (b->written < btree_blocks(b))

		bch_bset_init_next(&b->keys, write_block(b),

				   bset_magic(&b->c->sb));

	bch_btree_init_next(b);

}



static void bch_btree_node_write_sync(struct btree *b)
@@ -489,7 +506,11 @@ static void bch_btree_node_write_sync(struct btree *b) 
	struct closure cl;



	closure_init_stack(&cl);



	mutex_lock(&b->write_lock);

	bch_btree_node_write(b, &cl);

	mutex_unlock(&b->write_lock);



	closure_sync(&cl);

}
@@ -497,11 +518,10 @@ static void btree_node_write_work(struct work_struct *w) 
{

	struct btree *b = container_of(to_delayed_work(w), struct btree, work);



	rw_lock(true, b, b->level);



	mutex_lock(&b->write_lock);

	if (btree_node_dirty(b))

		bch_btree_node_write(b, NULL);

	rw_unlock(true, b);

		__bch_btree_node_write(b, NULL);

	mutex_unlock(&b->write_lock);

}



static void bch_btree_leaf_dirty(struct btree *b, atomic_t *journal_ref)
@@ -509,6 +529,8 @@ static void bch_btree_leaf_dirty(struct btree *b, atomic_t *journal_ref) 
	struct bset *i = btree_bset_last(b);

	struct btree_write *w = btree_current_write(b);



	lockdep_assert_held(&b->write_lock);



	BUG_ON(!b->written);

	BUG_ON(!i->keys);
@@ -593,6 +615,8 @@ static struct btree *mca_bucket_alloc(struct cache_set *c, 


	init_rwsem(&b->lock);

	lockdep_set_novalidate_class(&b->lock);

	mutex_init(&b->write_lock);

	lockdep_set_novalidate_class(&b->write_lock);

	INIT_LIST_HEAD(&b->list);

	INIT_DELAYED_WORK(&b->work, btree_node_write_work);

	b->c = c;
@@ -626,8 +650,12 @@ static int mca_reap(struct btree *b, unsigned min_order, bool flush) 
		up(&b->io_mutex);

	}



	mutex_lock(&b->write_lock);

	if (btree_node_dirty(b))

		bch_btree_node_write_sync(b);

		__bch_btree_node_write(b, &cl);

	mutex_unlock(&b->write_lock);



	closure_sync(&cl);



	/* wait for any in flight btree write */

	down(&b->io_mutex);
@@ -1010,10 +1038,14 @@ static void btree_node_free(struct btree *b) 


	BUG_ON(b == b->c->root);



	mutex_lock(&b->write_lock);



	if (btree_node_dirty(b))

		btree_complete_write(b, btree_current_write(b));

	clear_bit(BTREE_NODE_dirty, &b->flags);



	mutex_unlock(&b->write_lock);



	cancel_delayed_work(&b->work);



	mutex_lock(&b->c->bucket_lock);
@@ -1065,8 +1097,10 @@ static struct btree *btree_node_alloc_replacement(struct btree *b, bool wait) 
{

	struct btree *n = bch_btree_node_alloc(b->c, b->level, wait);

	if (!IS_ERR_OR_NULL(n)) {

		mutex_lock(&n->write_lock);

		bch_btree_sort_into(&b->keys, &n->keys, &b->c->sort);

		bkey_copy_key(&n->key, &b->key);

		mutex_unlock(&n->write_lock);

	}



	return n;
@@ -1269,6 +1303,9 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op, 
			goto out_nocoalesce;

	}



	for (i = 0; i < nodes; i++)

		mutex_lock(&new_nodes[i]->write_lock);



	for (i = nodes - 1; i > 0; --i) {

		struct bset *n1 = btree_bset_first(new_nodes[i]);

		struct bset *n2 = btree_bset_first(new_nodes[i - 1]);
@@ -1335,6 +1372,9 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op, 
		bch_keylist_add(keylist, &new_nodes[i]->key);

	}



	for (i = 0; i < nodes; i++)

		mutex_unlock(&new_nodes[i]->write_lock);



	closure_sync(&cl);



	/* We emptied out this node */
@@ -1399,7 +1439,6 @@ static unsigned btree_gc_count_keys(struct btree *b) 
static int btree_gc_recurse(struct btree *b, struct btree_op *op,

			    struct closure *writes, struct gc_stat *gc)

{

	unsigned i;

	int ret = 0;

	bool should_rewrite;

	struct btree *n;
@@ -1407,13 +1446,13 @@ static int btree_gc_recurse(struct btree *b, struct btree_op *op, 
	struct keylist keys;

	struct btree_iter iter;

	struct gc_merge_info r[GC_MERGE_NODES];

	struct gc_merge_info *last = r + GC_MERGE_NODES - 1;

	struct gc_merge_info *i, *last = r + ARRAY_SIZE(r) - 1;



	bch_keylist_init(&keys);

	bch_btree_iter_init(&b->keys, &iter, &b->c->gc_done);



	for (i = 0; i < GC_MERGE_NODES; i++)

		r[i].b = ERR_PTR(-EINTR);

	for (i = r; i < r + ARRAY_SIZE(r); i++)

		i->b = ERR_PTR(-EINTR);



	while (1) {

		k = bch_btree_iter_next_filter(&iter, &b->keys, bch_ptr_bad);
@@ -1443,6 +1482,7 @@ static int btree_gc_recurse(struct btree *b, struct btree_op *op, 


				if (!IS_ERR_OR_NULL(n)) {

					bch_btree_node_write_sync(n);



					bch_keylist_add(&keys, &n->key);



					make_btree_freeing_key(last->b,
@@ -1475,8 +1515,10 @@ static int btree_gc_recurse(struct btree *b, struct btree_op *op, 
			 * Must flush leaf nodes before gc ends, since replace

			 * operations aren't journalled

			 */

			mutex_lock(&last->b->write_lock);

			if (btree_node_dirty(last->b))

				bch_btree_node_write(last->b, writes);

			mutex_unlock(&last->b->write_lock);

			rw_unlock(true, last->b);

		}
@@ -1489,11 +1531,13 @@ static int btree_gc_recurse(struct btree *b, struct btree_op *op, 
		}

	}



	for (i = 0; i < GC_MERGE_NODES; i++)

		if (!IS_ERR_OR_NULL(r[i].b)) {

			if (btree_node_dirty(r[i].b))

				bch_btree_node_write(r[i].b, writes);

			rw_unlock(true, r[i].b);

	for (i = r; i < r + ARRAY_SIZE(r); i++)

		if (!IS_ERR_OR_NULL(i->b)) {

			mutex_lock(&i->b->write_lock);

			if (btree_node_dirty(i->b))

				bch_btree_node_write(i->b, writes);

			mutex_unlock(&i->b->write_lock);

			rw_unlock(true, i->b);

		}



	bch_keylist_free(&keys);
@@ -1514,6 +1558,7 @@ static int bch_btree_gc_root(struct btree *b, struct btree_op *op, 


		if (!IS_ERR_OR_NULL(n)) {

			bch_btree_node_write_sync(n);



			bch_btree_set_root(n);

			btree_node_free(b);

			rw_unlock(true, n);
@@ -1871,6 +1916,9 @@ static int btree_split(struct btree *b, struct btree_op *op, 
				goto err_free2;

		}



		mutex_lock(&n1->write_lock);

		mutex_lock(&n2->write_lock);



		bch_btree_insert_keys(n1, op, insert_keys, replace_key);



		/*
@@ -1897,21 +1945,26 @@ static int btree_split(struct btree *b, struct btree_op *op, 


		bch_keylist_add(&parent_keys, &n2->key);

		bch_btree_node_write(n2, &cl);

		mutex_unlock(&n2->write_lock);

		rw_unlock(true, n2);

	} else {

		trace_bcache_btree_node_compact(b, btree_bset_first(n1)->keys);



		mutex_lock(&n1->write_lock);

		bch_btree_insert_keys(n1, op, insert_keys, replace_key);

	}



	bch_keylist_add(&parent_keys, &n1->key);

	bch_btree_node_write(n1, &cl);

	mutex_unlock(&n1->write_lock);



	if (n3) {

		/* Depth increases, make a new root */

		mutex_lock(&n3->write_lock);

		bkey_copy_key(&n3->key, &MAX_KEY);

		bch_btree_insert_keys(n3, op, &parent_keys, NULL);

		bch_btree_node_write(n3, &cl);

		mutex_unlock(&n3->write_lock);



		closure_sync(&cl);

		bch_btree_set_root(n3);
@@ -1960,9 +2013,39 @@ static int bch_btree_insert_node(struct btree *b, struct btree_op *op, 
				 atomic_t *journal_ref,

				 struct bkey *replace_key)

{

	struct closure cl;



	BUG_ON(b->level && replace_key);



	closure_init_stack(&cl);



	mutex_lock(&b->write_lock);



	if (write_block(b) != btree_bset_last(b) &&

	    b->keys.last_set_unwritten)

		bch_btree_init_next(b); /* just wrote a set */



	if (bch_keylist_nkeys(insert_keys) > insert_u64s_remaining(b)) {

		mutex_unlock(&b->write_lock);

		goto split;

	}



	BUG_ON(write_block(b) != btree_bset_last(b));



	if (bch_btree_insert_keys(b, op, insert_keys, replace_key)) {

		if (!b->level)

			bch_btree_leaf_dirty(b, journal_ref);

		else

			bch_btree_node_write(b, &cl);

	}



	mutex_unlock(&b->write_lock);



	/* wait for btree node write if necessary, after unlock */

	closure_sync(&cl);



	return 0;

split:

	if (current->bio_list) {

		op->lock = b->c->root->level + 1;

		return -EAGAIN;
@@ -1973,20 +2056,11 @@ static int bch_btree_insert_node(struct btree *b, struct btree_op *op, 
		/* Invalidated all iterators */

		int ret = btree_split(b, op, insert_keys, replace_key);



			return bch_keylist_empty(insert_keys) ?

				0 : ret ?: -EINTR;

		}

	} else {

		BUG_ON(write_block(b) != btree_bset_last(b));



		if (bch_btree_insert_keys(b, op, insert_keys, replace_key)) {

			if (!b->level)

				bch_btree_leaf_dirty(b, journal_ref);

			else

				bch_btree_node_write_sync(b);

		}



		if (bch_keylist_empty(insert_keys))

			return 0;

		else if (!ret)

			return -EINTR;

		return ret;

	}

}

drivers/md/bcache/btree.h

+3 −0
Original line number Diff line number Diff line
@@ -127,6 +127,8 @@ struct btree { 
	struct cache_set	*c;

	struct btree		*parent;



	struct mutex		write_lock;



	unsigned long		flags;

	uint16_t		written;	/* would be nice to kill */

	uint8_t			level;
@@ -236,6 +238,7 @@ static inline void rw_unlock(bool w, struct btree *b) 
}



void bch_btree_node_read_done(struct btree *);

void __bch_btree_node_write(struct btree *, struct closure *);

void bch_btree_node_write(struct btree *, struct closure *);



void bch_btree_set_root(struct btree *);

drivers/md/bcache/journal.c

+4 −5
Original line number Diff line number Diff line
@@ -381,16 +381,15 @@ retry: 


	b = best;

	if (b) {

		rw_lock(true, b, b->level);



		mutex_lock(&b->write_lock);

		if (!btree_current_write(b)->journal) {

			rw_unlock(true, b);

			mutex_unlock(&b->write_lock);

			/* We raced */

			goto retry;

		}



		bch_btree_node_write(b, NULL);

		rw_unlock(true, b);

		__bch_btree_node_write(b, NULL);

		mutex_unlock(&b->write_lock);

	}

}

drivers/md/bcache/super.c

+7 −2
Original line number Diff line number Diff line
@@ -1398,9 +1398,12 @@ static void cache_set_flush(struct closure *cl) 
		list_add(&c->root->list, &c->btree_cache);



	/* Should skip this if we're unregistering because of an error */

	list_for_each_entry(b, &c->btree_cache, list)

	list_for_each_entry(b, &c->btree_cache, list) {

		mutex_lock(&b->write_lock);

		if (btree_node_dirty(b))

			bch_btree_node_write(b, NULL);

			__bch_btree_node_write(b, NULL);

		mutex_unlock(&b->write_lock);

	}



	for_each_cache(ca, c, i)

		if (ca->alloc_thread)
@@ -1667,8 +1670,10 @@ static void run_cache_set(struct cache_set *c) 
		if (IS_ERR_OR_NULL(c->root))

			goto err;



		mutex_lock(&c->root->write_lock);

		bkey_copy_key(&c->root->key, &MAX_KEY);

		bch_btree_node_write(c->root, &cl);

		mutex_unlock(&c->root->write_lock);



		bch_btree_set_root(c->root);

		rw_unlock(true, c->root);