[3.5.y.z extended stable] Patch "jbd2: don't BUG but return ENOSPC if a handle runs out of space" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    jbd2: don't BUG but return ENOSPC if a handle runs out of space

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From bc53fe8f253aede4b44e5c0b7e1761461e6c7565 Mon Sep 17 00:00:00 2001
From: Theodore Ts'o <tytso at mit.edu>
Date: Sun, 8 Dec 2013 21:12:59 -0500
Subject: jbd2: don't BUG but return ENOSPC if a handle runs out of space

commit f6c07cad081ba222d63623d913aafba5586c1d2c upstream.

If a handle runs out of space, we currently stop the kernel with a BUG
in jbd2_journal_dirty_metadata().  This makes it hard to figure out
what might be going on.  So return an error of ENOSPC, so we can let
the file system layer figure out what is going on, to make it more
likely we can get useful debugging information).  This should make it
easier to debug problems such as the one which was reported by:

    https://bugzilla.kernel.org/show_bug.cgi?id=44731

The only two callers of this function are ext4_handle_dirty_metadata()
and ocfs2_journal_dirty().  The ocfs2 function will trigger a
BUG_ON(), which means there will be no change in behavior.  The ext4
function will call ext4_error_inode() which will print the useful
debugging information and then handle the situation using ext4's error
handling mechanisms (i.e., which might mean halting the kernel or
remounting the file system read-only).

Also, since both file systems already call WARN_ON(), drop the WARN_ON
from jbd2_journal_dirty_metadata() to avoid two stack traces from
being displayed.

Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
Cc: ocfs2-devel at oss.oracle.com
Acked-by: Joel Becker <jlbec at evilplan.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/jbd2/transaction.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 81203d1..edfb1ec 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1126,7 +1126,10 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 		 * once a transaction -bzzz
 		 */
 		jh->b_modified = 1;
-		J_ASSERT_JH(jh, handle->h_buffer_credits > 0);
+		if (handle->h_buffer_credits <= 0) {
+			ret = -ENOSPC;
+			goto out_unlock_bh;
+		}
 		handle->h_buffer_credits--;
 	}

@@ -1209,7 +1212,6 @@ out_unlock_bh:
 	jbd2_journal_put_journal_head(jh);
 out:
 	JBUFFER_TRACE(jh, "exit");
-	WARN_ON(ret);	/* All errors are bugs, so dump the stack */
 	return ret;
 }

--
1.8.3.2