linux-ext4 - Re: [PATCH 5/7] jbd2: Don't call _

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Message-ID: <20191028160136.GC4404@mit.edu>
Date:   Mon, 28 Oct 2019 12:01:36 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Julia Cartwright <julia@...com>
Subject: Re: [PATCH 5/7] jbd2: Don't call __bforget() unnecessarily

On Mon, Oct 28, 2019 at 11:28:08AM -0400, Theodore Y. Ts'o wrote:
> drop:
> 	jbd_unlock_bh_state(bh);
> 	__brelse(bh);
> 	if (drop_reserve) {
> 		/* no need to reserve log space for this block -bzzz */
> 		handle->h_buffer_credits++;
> 	}
> 	return err;
> 
> not_jbd:
> 	jbd_unlock_bh_state(bh);
> 	__bforget(bh);
> 	goto drop;
> ----
> 
> And we still have a case we jump to not_jbd, at which point hilarity
> will ensue.
> 
> This is cleaned up in the following patch in this sequence, but this
> leaves us in a not-great state if we are ever bisecting.

Proposed fixup: I'll apply the following on top of this commit, and
then fix the merge conflicts in 6/7 so that the end result looks the
same as before.

Jan, any objections?  I figure this way it'll save you from resending
the patch series, since the rest of it looks fine to me.

							- Ted


diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index f2af4afc690a..c7c9a42451c7 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1541,8 +1541,11 @@ int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
 
 	jbd_lock_bh_state(bh);
 
-	if (!buffer_jbd(bh))
-		goto not_jbd;
+	if (!buffer_jbd(bh)) {
+		jbd_unlock_bh_state(bh);
+		__bforget(bh);
+		return 0;
+	}
 	jh = bh2jh(bh);
 
 	/* Critical error: attempting to delete a bitmap buffer, maybe?
@@ -1671,11 +1674,6 @@ int jbd2_journal_forget (handle_t *handle, struct buffer_head *bh)
 		handle->h_buffer_credits++;
 	}
 	return err;
-
-not_jbd:
-	jbd_unlock_bh_state(bh);
-	__bforget(bh);
-	goto drop;
 }
 
 /**