From bd2bb273a09b93e2a7d79d30458ab5f6f0b3757a Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Fri, 12 Jun 2020 22:29:48 -0400 Subject: [PATCH] bcachefs: Don't deadlock when btree node reuse changes lock ordering Btree node lock ordering is based on the logical key. However, 'struct btree' may be reused for a different btree node under memory pressure. This patch uses the new six lock callback to check if a btree node is no longer the node we wanted to lock before blocking. Signed-off-by: Kent Overstreet Signed-off-by: Kent Overstreet --- fs/bcachefs/btree_cache.c | 19 +++++++++++++-- fs/bcachefs/btree_iter.c | 38 +++++++++++++++++++++++------ fs/bcachefs/btree_locking.h | 19 +++++++++------ fs/bcachefs/btree_update_interior.c | 2 ++ 4 files changed, 62 insertions(+), 16 deletions(-) diff --git a/fs/bcachefs/btree_cache.c b/fs/bcachefs/btree_cache.c index d31017de53aad..9423cff1539ff 100644 --- a/fs/bcachefs/btree_cache.c +++ b/fs/bcachefs/btree_cache.c @@ -678,6 +678,14 @@ static noinline struct btree *bch2_btree_node_fill(struct bch_fs *c, return b; } +static int lock_node_check_fn(struct six_lock *lock, void *p) +{ + struct btree *b = container_of(lock, struct btree, c.lock); + const struct bkey_i *k = p; + + return b->hash_val == btree_ptr_hash_val(k) ? 0 : -1; +} + /** * bch_btree_node_get - find a btree node in the cache and lock it, reading it * in from disk if necessary. @@ -750,8 +758,12 @@ lock_node: if (btree_node_read_locked(iter, level + 1)) btree_node_unlock(iter, level + 1); - if (!btree_node_lock(b, k->k.p, level, iter, lock_type)) + if (!btree_node_lock(b, k->k.p, level, iter, lock_type, + lock_node_check_fn, (void *) k)) { + if (b->hash_val != btree_ptr_hash_val(k)) + goto retry; return ERR_PTR(-EINTR); + } if (unlikely(b->hash_val != btree_ptr_hash_val(k) || b->c.level != level || @@ -803,6 +815,7 @@ struct btree *bch2_btree_node_get_noiter(struct bch_fs *c, struct btree_cache *bc = &c->btree_cache; struct btree *b; struct bset_tree *t; + int ret; EBUG_ON(level >= BTREE_MAX_DEPTH); @@ -823,7 +836,9 @@ retry: return b; } else { lock_node: - six_lock_read(&b->c.lock, NULL, NULL); + ret = six_lock_read(&b->c.lock, lock_node_check_fn, (void *) k); + if (ret) + goto retry; if (unlikely(b->hash_val != btree_ptr_hash_val(k) || b->c.btree_id != btree_id || diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c index 35fe7db50fb50..b11c8e2a8d6b0 100644 --- a/fs/bcachefs/btree_iter.c +++ b/fs/bcachefs/btree_iter.c @@ -194,10 +194,13 @@ static inline bool btree_iter_get_locks(struct btree_iter *iter, /* Slowpath: */ bool __bch2_btree_node_lock(struct btree *b, struct bpos pos, unsigned level, struct btree_iter *iter, - enum six_lock_type type) + enum six_lock_type type, + six_lock_should_sleep_fn should_sleep_fn, + void *p) { struct btree_trans *trans = iter->trans; struct btree_iter *linked; + u64 start_time = local_clock(); bool ret = true; /* Check if it's safe to block: */ @@ -275,7 +278,14 @@ bool __bch2_btree_node_lock(struct btree *b, struct bpos pos, return false; } - __btree_node_lock_type(iter->trans->c, b, type); + if (six_trylock_type(&b->c.lock, type)) + return true; + + if (six_lock_type(&b->c.lock, type, should_sleep_fn, p)) + return false; + + bch2_time_stats_update(&trans->c->times[lock_to_time_stat(type)], + start_time); return true; } @@ -286,6 +296,11 @@ static void bch2_btree_iter_verify_locks(struct btree_iter *iter) { unsigned l; + if (!(iter->trans->iters_linked & (1ULL << iter->idx))) { + BUG_ON(iter->nodes_locked); + return; + } + for (l = 0; btree_iter_node(iter, l); l++) { if (iter->uptodate >= BTREE_ITER_NEED_RELOCK && !btree_node_locked(iter, l)) @@ -300,7 +315,7 @@ void bch2_btree_trans_verify_locks(struct btree_trans *trans) { struct btree_iter *iter; - trans_for_each_iter(trans, iter) + trans_for_each_iter_all(trans, iter) bch2_btree_iter_verify_locks(iter); } #else @@ -892,18 +907,26 @@ void bch2_btree_iter_reinit_node(struct btree_iter *iter, struct btree *b) __btree_iter_init(linked, b->c.level); } +static int lock_root_check_fn(struct six_lock *lock, void *p) +{ + struct btree *b = container_of(lock, struct btree, c.lock); + struct btree **rootp = p; + + return b == *rootp ? 0 : -1; +} + static inline int btree_iter_lock_root(struct btree_iter *iter, unsigned depth_want) { struct bch_fs *c = iter->trans->c; - struct btree *b; + struct btree *b, **rootp = &c->btree_roots[iter->btree_id].b; enum six_lock_type lock_type; unsigned i; EBUG_ON(iter->nodes_locked); while (1) { - b = READ_ONCE(c->btree_roots[iter->btree_id].b); + b = READ_ONCE(*rootp); iter->level = READ_ONCE(b->c.level); if (unlikely(iter->level < depth_want)) { @@ -921,10 +944,11 @@ static inline int btree_iter_lock_root(struct btree_iter *iter, lock_type = __btree_lock_want(iter, iter->level); if (unlikely(!btree_node_lock(b, POS_MAX, iter->level, - iter, lock_type))) + iter, lock_type, + lock_root_check_fn, rootp))) return -EINTR; - if (likely(b == c->btree_roots[iter->btree_id].b && + if (likely(b == READ_ONCE(*rootp) && b->c.level == iter->level && !race_fault())) { for (i = 0; i < iter->level; i++) diff --git a/fs/bcachefs/btree_locking.h b/fs/bcachefs/btree_locking.h index 4c80ab368e699..ffee6f2d7d4b6 100644 --- a/fs/bcachefs/btree_locking.h +++ b/fs/bcachefs/btree_locking.h @@ -174,17 +174,21 @@ static inline bool btree_node_lock_increment(struct btree_trans *trans, } bool __bch2_btree_node_lock(struct btree *, struct bpos, unsigned, - struct btree_iter *, enum six_lock_type); - -static inline bool btree_node_lock(struct btree *b, struct bpos pos, - unsigned level, - struct btree_iter *iter, - enum six_lock_type type) + struct btree_iter *, enum six_lock_type, + six_lock_should_sleep_fn, void *); + +static inline bool btree_node_lock(struct btree *b, + struct bpos pos, unsigned level, + struct btree_iter *iter, + enum six_lock_type type, + six_lock_should_sleep_fn should_sleep_fn, void *p) { struct btree_trans *trans = iter->trans; bool ret; EBUG_ON(level >= BTREE_MAX_DEPTH); + EBUG_ON(!(trans->iters_linked & (1ULL << iter->idx))); + #ifdef CONFIG_BCACHEFS_DEBUG trans->locking = b; trans->locking_iter_idx = iter->idx; @@ -194,7 +198,8 @@ static inline bool btree_node_lock(struct btree *b, struct bpos pos, #endif ret = likely(six_trylock_type(&b->c.lock, type)) || btree_node_lock_increment(trans, b, level, type) || - __bch2_btree_node_lock(b, pos, level, iter, type); + __bch2_btree_node_lock(b, pos, level, iter, type, + should_sleep_fn, p); #ifdef CONFIG_BCACHEFS_DEBUG trans->locking = NULL; diff --git a/fs/bcachefs/btree_update_interior.c b/fs/bcachefs/btree_update_interior.c index bb921852a0932..2d68f4eaca342 100644 --- a/fs/bcachefs/btree_update_interior.c +++ b/fs/bcachefs/btree_update_interior.c @@ -135,6 +135,8 @@ static void __btree_node_free(struct bch_fs *c, struct btree *b) bch2_btree_node_hash_remove(&c->btree_cache, b); + six_lock_wakeup_all(&b->c.lock); + mutex_lock(&c->btree_cache.lock); list_move(&b->list, &c->btree_cache.freeable); mutex_unlock(&c->btree_cache.lock); -- 2.30.2