Patch "jbd2: Fix lockdep splat with generic/270 test" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

jbd2: Fix lockdep splat with generic/270 test

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
jbd2-fix-lockdep-splat-with-generic-270-test.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Sat, 29 Apr 2017 20:12:16 -0400
Subject: jbd2: Fix lockdep splat with generic/270 test

From: Jan Kara <[email protected]>

[ Upstream commit c52c47e4b4fbe4284602fc2ccbfc4a4d8dc05b49 ]

I've hit a lockdep splat with generic/270 test complaining that:

3216.fsstress.b/3533 is trying to acquire lock:
(jbd2_handle){++++..}, at: [<ffffffff813152e0>] jbd2_log_wait_commit+0x0/0x150

but task is already holding lock:
(jbd2_handle){++++..}, at: [<ffffffff8130bd3b>] start_this_handle+0x35b/0x850

The underlying problem is that jbd2_journal_force_commit_nested() (called from ext4_should_retry_alloc()) may get called while a transaction handle is started. In such case it takes care to not wait for commit of the running transaction (which would deadlock) but only for a commit of a transaction that is already committing (which is safe as that doesn't wait for any filesystem locks).

In fact there are also other callers of jbd2_log_wait_commit() that take care to pass tid of a transaction that is already committing and for those cases, the lockdep instrumentation is too restrictive and leading to false positive reports. Fix the problem by calling jbd2_might_wait_for_commit() from jbd2_log_wait_commit() only if the transaction isn't already committing.

---
 fs/jbd2/journal.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

@@ -691,8 +691,21 @@ int jbd2_log_wait_commit(journal_t *jour
 {
 	int err = 0;
 
-	jbd2_might_wait_for_commit(journal);
 	read_lock(&journal->j_state_lock);
+#ifdef CONFIG_PROVE_LOCKING
+	/*
+	 * Some callers make sure transaction is already committing and in that
+	 * case we cannot block on open handles anymore. So don't warn in that
+	 * case.
+	 */
+	if (tid_gt(tid, journal->j_commit_sequence) &&
+	    (!journal->j_committing_transaction ||
+	     journal->j_committing_transaction->t_tid != tid)) {
+		read_unlock(&journal->j_state_lock);
+		jbd2_might_wait_for_commit(journal);
+		read_lock(&journal->j_state_lock);
+	}
+#endif
 #ifdef CONFIG_JBD2_DEBUG
 	if (!tid_geq(journal->j_commit_request, tid)) {
 		printk(KERN_ERR

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/jbd2-fix-lockdep-splat-with-generic-270-test.patch