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bcachefs: Ensure srcu lock is not held too long

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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 <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2023-10-30 12:30:52 -04:00
parent 6dfa10ab22
commit c4accde498
4 changed files with 40 additions and 13 deletions
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42
fs/bcachefs/btree_iter.c
View File

@ -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);

4
fs/bcachefs/btree_iter.h
View File

@ -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 *);
/*

6
fs/bcachefs/btree_locking.c
View File

@ -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;

1
fs/bcachefs/btree_types.h
View File

@ -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;