Commit c4accde4 authored by Kent Overstreet's avatar Kent Overstreet
Browse files

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: default avatarKent Overstreet <kent.overstreet@linux.dev>
parent 6dfa10ab

fs/bcachefs/btree_iter.c

+29 −13
Original line number Diff line number Diff line
@@ -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:
@@ -2830,8 +2833,9 @@ 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)

{

	if (trans->srcu_held) {

		struct bch_fs *c = trans->c;

		struct btree_path *path;
@@ -2840,8 +2844,17 @@ static noinline void bch2_trans_reset_srcu_lock(struct btree_trans *trans) 
				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_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) {
@@ -2983,6 +2997,7 @@ struct btree_trans *__bch2_trans_get(struct bch_fs *c, unsigned fn_idx) 


	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;
@@ -3059,6 +3074,7 @@ void bch2_trans_put(struct btree_trans *trans) 


	check_btree_paths_leaked(trans);



	if (trans->srcu_held)

		srcu_read_unlock(&c->btree_trans_barrier, trans->srcu_idx);



	bch2_journal_preres_put(&c->journal, &trans->journal_preres);

fs/bcachefs/btree_iter.h

+4 −0
Original line number Diff line number Diff line
@@ -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 *);



/*

fs/bcachefs/btree_locking.c

+6 −0
Original line number Diff line number Diff line
@@ -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;

fs/bcachefs/btree_types.h

+1 −0
Original line number Diff line number Diff line
@@ -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;