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bcachefs: Avoid using btree_node_lock_nopath()

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With the upcoming cycle detector, we have to be careful about using
btree_node_lock_nopath - in particular, using it to take write locks can
cause deadlocks.

All held locks need to be tracked in a btree_path, so that the cycle
detector knows about them - unless we know that we cannot cause
deadlocks for other reasons: e.g. we are only taking read locks, or
we're in very early fsck (topology repair).

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2022-09-02 22:59:39 -04:00
parent 3d21d48e89
commit 38474c2642
3 changed files with 30 additions and 40 deletions
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6
fs/bcachefs/btree_iter.c
View file

@ -716,13 +716,13 @@ void bch2_trans_node_add(struct btree_trans *trans, struct btree *b)
struct btree_path *path;
trans_for_each_path(trans, path)
if (!path->cached &&
if (path->uptodate == BTREE_ITER_UPTODATE &&
!path->cached &&
btree_path_pos_in_node(path, b)) {
enum btree_node_locked_type t =
btree_lock_want(path, b->c.level);
if (path->nodes_locked &&
t != BTREE_NODE_UNLOCKED) {
if (t != BTREE_NODE_UNLOCKED) {
btree_node_unlock(trans, path, b->c.level);
six_lock_increment(&b->c.lock, (enum six_lock_type) t);
mark_btree_node_locked(trans, path, b->c.level, (enum six_lock_type) t);

17
fs/bcachefs/btree_key_cache.c
View file

@ -568,26 +568,21 @@ static int btree_key_cache_flush_pos(struct btree_trans *trans,
atomic_long_dec(&c->btree_key_cache.nr_dirty);
}
} else {
struct btree_path *path2;
evict:
BUG_ON(!btree_node_intent_locked(c_iter.path, 0));
trans_for_each_path(trans, path2)
if (path2 != c_iter.path)
__bch2_btree_path_unlock(trans, path2);
/*
* XXX: holding a lock that is not marked in btree_trans, not
* ideal:
*/
six_lock_increment(&ck->c.lock, SIX_LOCK_intent);
bch2_trans_unlock(trans);
/* Will not fail because we are holding no other locks: */
btree_node_lock_nopath_nofail(trans, &ck->c, SIX_LOCK_write);
bch2_btree_node_lock_write_nofail(trans, c_iter.path, &ck->c);
if (test_bit(BKEY_CACHED_DIRTY, &ck->flags)) {
clear_bit(BKEY_CACHED_DIRTY, &ck->flags);
atomic_long_dec(&c->btree_key_cache.nr_dirty);
}
mark_btree_node_locked_noreset(c_iter.path, 0, BTREE_NODE_UNLOCKED);
bkey_cached_evict(&c->btree_key_cache, ck);
bkey_cached_free_fast(&c->btree_key_cache, ck);
}
out:

47
fs/bcachefs/btree_update_interior.c
View file

@ -160,22 +160,23 @@ static void __btree_node_free(struct bch_fs *c, struct btree *b)
}
static void bch2_btree_node_free_inmem(struct btree_trans *trans,
struct btree_path *path,
struct btree *b)
{
struct bch_fs *c = trans->c;
struct btree_path *path;
trans_for_each_path(trans, path)
BUG_ON(path->l[b->c.level].b == b &&
path->l[b->c.level].lock_seq == b->c.lock.state.seq);
btree_node_lock_nopath_nofail(trans, &b->c, SIX_LOCK_write);
unsigned level = b->c.level;
bch2_btree_node_lock_write_nofail(trans, path, &b->c);
bch2_btree_node_hash_remove(&c->btree_cache, b);
__btree_node_free(c, b);
six_unlock_write(&b->c.lock);
six_unlock_intent(&b->c.lock);
mark_btree_node_locked_noreset(path, level, SIX_LOCK_intent);
trans_for_each_path(trans, path)
if (path->l[level].b == b) {
btree_node_unlock(trans, path, level);
path->l[level].b = ERR_PTR(-BCH_ERR_no_btree_node_init);
}
}
static struct btree *__bch2_btree_node_alloc(struct btree_trans *trans,
@ -1507,22 +1508,19 @@ static void btree_split(struct btree_update *as, struct btree_trans *trans,
if (n3)
bch2_btree_update_get_open_buckets(as, n3);
/* Successful split, update the path to point to the new nodes: */
six_lock_increment(&b->c.lock, SIX_LOCK_intent);
if (n3)
bch2_trans_node_add(trans, n3);
if (n2)
bch2_trans_node_add(trans, n2);
bch2_trans_node_add(trans, n1);
/*
* The old node must be freed (in memory) _before_ unlocking the new
* nodes - else another thread could re-acquire a read lock on the old
* node after another thread has locked and updated the new node, thus
* seeing stale data:
*/
bch2_btree_node_free_inmem(trans, b);
bch2_btree_node_free_inmem(trans, path, b);
if (n3)
bch2_trans_node_add(trans, n3);
if (n2)
bch2_trans_node_add(trans, n2);
bch2_trans_node_add(trans, n1);
if (n3)
six_unlock_intent(&n3->c.lock);
@ -1785,16 +1783,13 @@ int __bch2_foreground_maybe_merge(struct btree_trans *trans,
bch2_btree_update_get_open_buckets(as, n);
six_lock_increment(&b->c.lock, SIX_LOCK_intent);
six_lock_increment(&m->c.lock, SIX_LOCK_intent);
bch2_btree_node_free_inmem(trans, path, b);
bch2_btree_node_free_inmem(trans, sib_path, m);
bch2_trans_node_add(trans, n);
bch2_trans_verify_paths(trans);
bch2_btree_node_free_inmem(trans, b);
bch2_btree_node_free_inmem(trans, m);
six_unlock_intent(&n->c.lock);
bch2_btree_update_done(as, trans);
@ -1851,9 +1846,9 @@ int bch2_btree_node_rewrite(struct btree_trans *trans,
bch2_btree_update_get_open_buckets(as, n);
six_lock_increment(&b->c.lock, SIX_LOCK_intent);
bch2_btree_node_free_inmem(trans, iter->path, b);
bch2_trans_node_add(trans, n);
bch2_btree_node_free_inmem(trans, b);
six_unlock_intent(&n->c.lock);
bch2_btree_update_done(as, trans);