linux-ext4 - [PATCH 2/2] jbd2: add sparse annotations for add_transaction

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Date:   Sat, 14 Aug 2021 10:59:00 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 2/2] jbd2: add sparse annotations for add_transaction_credits()

Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 fs/jbd2/transaction.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 8804e126805f..5347411ae13e 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -223,9 +223,15 @@ static void sub_reserved_credits(journal_t *journal, int blocks)
  * with j_state_lock held for reading. Returns 0 if handle joined the running
  * transaction. Returns 1 if we had to wait, j_state_lock is dropped, and
  * caller must retry.
+ *
+ * Note: because j_state_lock may be dropped depending on the return
+ * value, we need to fake out sparse so ti doesn't complain about a
+ * locking imbalance.  Callers of add_transaction_credits will need to
+ * make a similar accomodation.
  */
 static int add_transaction_credits(journal_t *journal, int blocks,
 				   int rsv_blocks)
+__must_hold(&journal->j_state_lock)
 {
 	transaction_t *t = journal->j_running_transaction;
 	int needed;
@@ -238,6 +244,7 @@ static int add_transaction_credits(journal_t *journal, int blocks,
 	if (t->t_state != T_RUNNING) {
 		WARN_ON_ONCE(t->t_state >= T_FLUSH);
 		wait_transaction_locked(journal);
+		__acquire(&journal->j_state_lock); /* fake out sparse */
 		return 1;
 	}
 
@@ -266,10 +273,12 @@ static int add_transaction_credits(journal_t *journal, int blocks,
 			wait_event(journal->j_wait_reserved,
 				   atomic_read(&journal->j_reserved_credits) + total <=
 				   journal->j_max_transaction_buffers);
+			__acquire(&journal->j_state_lock); /* fake out sparse */
 			return 1;
 		}
 
 		wait_transaction_locked(journal);
+		__acquire(&journal->j_state_lock); /* fake out sparse */
 		return 1;
 	}
 
@@ -293,6 +302,7 @@ static int add_transaction_credits(journal_t *journal, int blocks,
 					journal->j_max_transaction_buffers)
 			__jbd2_log_wait_for_space(journal);
 		write_unlock(&journal->j_state_lock);
+		__acquire(&journal->j_state_lock); /* fake out sparse */
 		return 1;
 	}
 
@@ -310,6 +320,7 @@ static int add_transaction_credits(journal_t *journal, int blocks,
 		wait_event(journal->j_wait_reserved,
 			 atomic_read(&journal->j_reserved_credits) + rsv_blocks
 			 <= journal->j_max_transaction_buffers / 2);
+		__acquire(&journal->j_state_lock); /* fake out sparse */
 		return 1;
 	}
 	return 0;
@@ -413,8 +424,14 @@ static int start_this_handle(journal_t *journal, handle_t *handle,
 
 	if (!handle->h_reserved) {
 		/* We may have dropped j_state_lock - restart in that case */
-		if (add_transaction_credits(journal, blocks, rsv_blocks))
+		if (add_transaction_credits(journal, blocks, rsv_blocks)) {
+			/*
+			 * add_transaction_credits releases
+			 * j_state_lock on a non-zero return
+			 */
+			__release(&journal->j_state_lock);
 			goto repeat;
+		}
 	} else {
 		/*
 		 * We have handle reserved so we are allowed to join T_LOCKED
-- 
2.31.0