From c4accde498dd7db8352d574958d19a5f710aba69 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Mon, 30 Oct 2023 12:30:52 -0400 Subject: [PATCH] bcachefs: Ensure srcu lock is not held too long The SRCU read lock that btree_trans takes exists to make it safe for bch2_trans_relock() to deref pointers to btree nodes/key cache items we don't have locked, but as a side effect it blocks reclaim from freeing those items. Thus, it's important to not hold it for too long: we need to differentiate between bch2_trans_unlock() calls that will be only for a short duration, and ones that will be for an unbounded duration. This introduces bch2_trans_unlock_long(), to be used mainly by the data move paths. Signed-off-by: Kent Overstreet --- fs/bcachefs/btree_iter.c | 42 +++++++++++++++++++++++++------------ fs/bcachefs/btree_iter.h | 4 ++++ fs/bcachefs/btree_locking.c | 6 ++++++ fs/bcachefs/btree_types.h | 1 + 4 files changed, 40 insertions(+), 13 deletions(-) diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c index 0622f729411fd..b22fd395a1fd7 100644 --- a/fs/bcachefs/btree_iter.c +++ b/fs/bcachefs/btree_iter.c @@ -1109,6 +1109,9 @@ int bch2_btree_path_traverse_one(struct btree_trans *trans, if (unlikely(ret)) goto out; + if (unlikely(!trans->srcu_held)) + bch2_trans_srcu_lock(trans); + /* * Ensure we obey path->should_be_locked: if it's set, we can't unlock * and re-traverse the path without a transaction restart: @@ -2830,18 +2833,28 @@ void *__bch2_trans_kmalloc(struct btree_trans *trans, size_t size) return p; } -static noinline void bch2_trans_reset_srcu_lock(struct btree_trans *trans) +void bch2_trans_srcu_unlock(struct btree_trans *trans) { - struct bch_fs *c = trans->c; - struct btree_path *path; + if (trans->srcu_held) { + struct bch_fs *c = trans->c; + struct btree_path *path; - trans_for_each_path(trans, path) - if (path->cached && !btree_node_locked(path, 0)) - path->l[0].b = ERR_PTR(-BCH_ERR_no_btree_node_srcu_reset); + trans_for_each_path(trans, path) + if (path->cached && !btree_node_locked(path, 0)) + path->l[0].b = ERR_PTR(-BCH_ERR_no_btree_node_srcu_reset); - srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx); - trans->srcu_idx = srcu_read_lock(&c->btree_trans_barrier); - trans->srcu_lock_time = jiffies; + srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx); + trans->srcu_held = false; + } +} + +void bch2_trans_srcu_lock(struct btree_trans *trans) +{ + if (!trans->srcu_held) { + trans->srcu_idx = srcu_read_lock(&trans->c->btree_trans_barrier); + trans->srcu_lock_time = jiffies; + trans->srcu_held = true; + } } /** @@ -2895,8 +2908,9 @@ u32 bch2_trans_begin(struct btree_trans *trans) } trans->last_begin_time = now; - if (unlikely(time_after(jiffies, trans->srcu_lock_time + msecs_to_jiffies(10)))) - bch2_trans_reset_srcu_lock(trans); + if (unlikely(trans->srcu_held && + time_after(jiffies, trans->srcu_lock_time + msecs_to_jiffies(10)))) + bch2_trans_srcu_unlock(trans); trans->last_begin_ip = _RET_IP_; if (trans->restarted) { @@ -2981,8 +2995,9 @@ struct btree_trans *__bch2_trans_get(struct bch_fs *c, unsigned fn_idx) trans->wb_updates_size = s->wb_updates_size; } - trans->srcu_idx = srcu_read_lock(&c->btree_trans_barrier); + trans->srcu_idx = srcu_read_lock(&c->btree_trans_barrier); trans->srcu_lock_time = jiffies; + trans->srcu_held = true; if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG_TRANSACTIONS)) { struct btree_trans *pos; @@ -3059,7 +3074,8 @@ void bch2_trans_put(struct btree_trans *trans) check_btree_paths_leaked(trans); - srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx); + if (trans->srcu_held) + srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx); bch2_journal_preres_put(&c->journal, &trans->journal_preres); diff --git a/fs/bcachefs/btree_iter.h b/fs/bcachefs/btree_iter.h index 70759ee3e5c73..5e103f519e62e 100644 --- a/fs/bcachefs/btree_iter.h +++ b/fs/bcachefs/btree_iter.h @@ -274,6 +274,7 @@ void bch2_path_put(struct btree_trans *, struct btree_path *, bool); int bch2_trans_relock(struct btree_trans *); int bch2_trans_relock_notrace(struct btree_trans *); void bch2_trans_unlock(struct btree_trans *); +void bch2_trans_unlock_long(struct btree_trans *); bool bch2_trans_locked(struct btree_trans *); static inline int trans_was_restarted(struct btree_trans *trans, u32 restart_count) @@ -579,6 +580,9 @@ static inline int __bch2_bkey_get_val_typed(struct btree_trans *trans, __bch2_bkey_get_val_typed(_trans, _btree_id, _pos, _flags, \ KEY_TYPE_##_type, sizeof(*_val), _val) +void bch2_trans_srcu_unlock(struct btree_trans *); +void bch2_trans_srcu_lock(struct btree_trans *); + u32 bch2_trans_begin(struct btree_trans *); /* diff --git a/fs/bcachefs/btree_locking.c b/fs/bcachefs/btree_locking.c index bc45cd2a34a41..3d48834d091fb 100644 --- a/fs/bcachefs/btree_locking.c +++ b/fs/bcachefs/btree_locking.c @@ -753,6 +753,12 @@ void bch2_trans_unlock(struct btree_trans *trans) __bch2_btree_path_unlock(trans, path); } +void bch2_trans_unlock_long(struct btree_trans *trans) +{ + bch2_trans_unlock(trans); + bch2_trans_srcu_unlock(trans); +} + bool bch2_trans_locked(struct btree_trans *trans) { struct btree_path *path; diff --git a/fs/bcachefs/btree_types.h b/fs/bcachefs/btree_types.h index ecbb44b939a05..7cc8d6b12161b 100644 --- a/fs/bcachefs/btree_types.h +++ b/fs/bcachefs/btree_types.h @@ -426,6 +426,7 @@ struct btree_trans { u8 nr_updates; u8 nr_wb_updates; u8 wb_updates_size; + bool srcu_held:1; bool used_mempool:1; bool in_traverse_all:1; bool paths_sorted:1; -- 2.30.2