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: Kent Overstreet <kmo@daterainc.com>
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index e83732e..01b1b7e 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -167,6 +167,20 @@
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 @@
}
}
-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 @@
&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 @@
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 @@
{
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 @@
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 @@
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 @@
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 @@
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 @@
{
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 @@
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 @@
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 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 @@
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 @@
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 @@
* 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 @@
}
}
- 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 @@
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 @@
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 @@
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);
@@ -1960,33 +2013,54 @@
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)) {
- if (current->bio_list) {
- op->lock = b->c->root->level + 1;
- return -EAGAIN;
- } else if (op->lock <= b->c->root->level) {
- op->lock = b->c->root->level + 1;
- return -EINTR;
- } else {
- /* Invalidated all iterators */
- int ret = btree_split(b, op, insert_keys, replace_key);
+ mutex_unlock(&b->write_lock);
+ goto split;
+ }
- return bch_keylist_empty(insert_keys) ?
- 0 : ret ?: -EINTR;
- }
+ 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;
+ } else if (op->lock <= b->c->root->level) {
+ op->lock = b->c->root->level + 1;
+ return -EINTR;
} else {
- BUG_ON(write_block(b) != btree_bset_last(b));
+ /* Invalidated all iterators */
+ int ret = btree_split(b, op, insert_keys, replace_key);
- 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);
- }
-
- return 0;
+ if (bch_keylist_empty(insert_keys))
+ return 0;
+ else if (!ret)
+ return -EINTR;
+ return ret;
}
}
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
index def9dc4..acebf26 100644
--- a/drivers/md/bcache/btree.h
+++ b/drivers/md/bcache/btree.h
@@ -127,6 +127,8 @@
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 @@
}
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 *);
diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index c8bfc28..59e8202 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -381,16 +381,15 @@
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);
}
}
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index ddfde38..9ded064 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1398,9 +1398,12 @@
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 @@
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);