linux-ext4 - [PATCH 2/2] Updated locking documentation for journal

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Date:   Wed, 10 Feb 2021 10:57:38 +0100
From:   Alexander Lochmann <alexander.lochmann@...dortmund.de>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Alexander Lochmann <alexander.lochmann@...dortmund.de>,
        Horst Schirmeier <horst.schirmeier@...dortmund.de>,
        "Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.com>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] Updated locking documentation for journal_t

Some members of transaction_t are allowed to be read without
any lock being held if consistency doesn't matter.
Based on LockDoc's findings, we extended the locking
documentation of those members.
Each one of them is marked with a short comment:
"no lock for quick racy checks".

Signed-off-by: Alexander Lochmann <alexander.lochmann@...dortmund.de>
Signed-off-by: Horst Schirmeier <horst.schirmeier@...dortmund.de>
---
 include/linux/jbd2.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 18f77d9b1745..4dca33a063dd 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -768,7 +768,7 @@ enum passtype {PASS_SCAN, PASS_REVOKE, PASS_REPLAY};
 struct journal_s
 {
 	/**
-	 * @j_flags: General journaling state flags [j_state_lock]
+	 * @j_flags: General journaling state flags [j_state_lock, no lock for quick racy checks]
 	 */
 	unsigned long		j_flags;
 
@@ -808,7 +808,7 @@ struct journal_s
 	/**
 	 * @j_barrier_count:
 	 *
-	 * Number of processes waiting to create a barrier lock [j_state_lock]
+	 * Number of processes waiting to create a barrier lock [j_state_lock, no lock for quick racy checks]
 	 */
 	int			j_barrier_count;
 
@@ -821,7 +821,7 @@ struct journal_s
 	 * @j_running_transaction:
 	 *
 	 * Transactions: The current running transaction...
-	 * [j_state_lock] [caller holding open handle]
+	 * [j_state_lock, no lock for quick racy checks] [caller holding open handle]
 	 */
 	transaction_t		*j_running_transaction;
 
@@ -1033,7 +1033,7 @@ struct journal_s
 	 * @j_commit_sequence:
 	 *
 	 * Sequence number of the most recently committed transaction
-	 * [j_state_lock].
+	 * [j_state_lock, no lock for quick racy checks].
 	 */
 	tid_t			j_commit_sequence;
 
@@ -1041,7 +1041,7 @@ struct journal_s
 	 * @j_commit_request:
 	 *
 	 * Sequence number of the most recent transaction wanting commit
-	 * [j_state_lock]
+	 * [j_state_lock, no lock for quick racy checks]
 	 */
 	tid_t			j_commit_request;
 
-- 
2.20.1