bcachefs: optimize __bch2_trans_get(), kill DEBUG_TRANSACTIONS

 - Some tweaks to greatly reduce locking overhead for the list of btree
   transactions, so that it can always be enabled: leave btree_trans
   objects on the list when they're on the percpu single item freelist,
   and only check for duplicates in the same process when
   CONFIG_BCACHEFS_DEBUG is enabled

 - don't zero out the full btree_trans() unless we allocated it from
   the mempool

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 9 insertions, 9 deletions

diff --git a/fs/bcachefs/debug.c b/fs/bcachefs/debug.c
index bbf6fce3a789..c0b4d9057f29 100644
--- a/fs/bcachefs/debug.c
+++ b/fs/bcachefs/debug.c
@@ -592,7 +592,6 @@ static const struct file_operations cached_btree_nodes_ops = {
 	.read		= bch2_cached_btree_nodes_read,
 };
 
-#ifdef CONFIG_BCACHEFS_DEBUG_TRANSACTIONS
 static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf,
 					    size_t size, loff_t *ppos)
 {
@@ -608,7 +607,9 @@ static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf,
 restart:
 	seqmutex_lock(&c->btree_trans_lock);
 	list_for_each_entry(trans, &c->btree_trans_list, list) {
-		if (trans->locking_wait.task->pid <= i->iter)
+		struct task_struct *task = READ_ONCE(trans->locking_wait.task);
+
+		if (!task || task->pid <= i->iter)
 			continue;
 
 		closure_get(&trans->ref);
@@ -626,11 +627,11 @@ restart:
 		prt_printf(&i->buf, "backtrace:");
 		prt_newline(&i->buf);
 		printbuf_indent_add(&i->buf, 2);
-		bch2_prt_task_backtrace(&i->buf, trans->locking_wait.task);
+		bch2_prt_task_backtrace(&i->buf, task);
 		printbuf_indent_sub(&i->buf, 2);
 		prt_newline(&i->buf);
 
-		i->iter = trans->locking_wait.task->pid;
+		i->iter = task->pid;
 
 		closure_put(&trans->ref);
 
@@ -654,7 +655,6 @@ static const struct file_operations btree_transactions_ops = {
 	.release	= bch2_dump_release,
 	.read		= bch2_btree_transactions_read,
 };
-#endif /* CONFIG_BCACHEFS_DEBUG_TRANSACTIONS */
 
 static ssize_t bch2_journal_pins_read(struct file *file, char __user *buf,
 				      size_t size, loff_t *ppos)
@@ -811,7 +811,9 @@ static ssize_t bch2_btree_deadlock_read(struct file *file, char __user *buf,
 restart:
 	seqmutex_lock(&c->btree_trans_lock);
 	list_for_each_entry(trans, &c->btree_trans_list, list) {
-		if (trans->locking_wait.task->pid <= i->iter)
+		struct task_struct *task = READ_ONCE(trans->locking_wait.task);
+
+		if (!task || task->pid <= i->iter)
 			continue;
 
 		closure_get(&trans->ref);
@@ -826,7 +828,7 @@ restart:
 
 		bch2_check_for_deadlock(trans, &i->buf);
 
-		i->iter = trans->locking_wait.task->pid;
+		i->iter = task->pid;
 
 		closure_put(&trans->ref);
 
@@ -873,10 +875,8 @@ void bch2_fs_debug_init(struct bch_fs *c)
 	debugfs_create_file("cached_btree_nodes", 0400, c->fs_debug_dir,
 			    c->btree_debug, &cached_btree_nodes_ops);
 
-#ifdef CONFIG_BCACHEFS_DEBUG_TRANSACTIONS
 	debugfs_create_file("btree_transactions", 0400, c->fs_debug_dir,
 			    c->btree_debug, &btree_transactions_ops);
-#endif
 
 	debugfs_create_file("journal_pins", 0400, c->fs_debug_dir,
 			    c->btree_debug, &journal_pins_ops);