linux-ext4 - [PATCH] jbd2: Add sanity check for attempts to start handle during umount

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Message-Id: <1286051806-11641-1-git-send-email-tytso@mit.edu>
Date:	Sat,  2 Oct 2010 16:36:46 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Theodore Ts'o <tytso@....edu>
Subject: [PATCH] jbd2: Add sanity check for attempts to start handle during umount

If there is an attempt to modify the file system during the call to
jbd2_destroy_journal(), it can lead to a system lockup.  So add some
checking to make it much more obvious when this happens to and to
determine where the offending code is located.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
 fs/jbd2/checkpoint.c  |   10 ++++++++++
 fs/jbd2/transaction.c |    1 +
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/fs/jbd2/checkpoint.c b/fs/jbd2/checkpoint.c
index 5247e7f..524800d 100644
--- a/fs/jbd2/checkpoint.c
+++ b/fs/jbd2/checkpoint.c
@@ -299,6 +299,16 @@ static int __process_buffer(journal_t *journal, struct journal_head *jh,
 		transaction->t_chp_stats.cs_forced_to_close++;
 		spin_unlock(&journal->j_list_lock);
 		jbd_unlock_bh_state(bh);
+		if (unlikely(journal->j_flags & JBD2_UNMOUNT))
+			/*
+			 * The journal thread is dead; so starting and
+			 * waiting for a commit to finish will cause
+			 * us to wait for a _very_ long time.
+			 */
+			printk(KERN_ERR "JBD2: %s: "
+			       "Waiting for Godot: block %llu\n",
+			       journal->j_devname,
+			       (unsigned long long) bh->b_blocknr);
 		jbd2_log_start_commit(journal, tid);
 		jbd2_log_wait_commit(journal, tid);
 		ret = 1;
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index f3479d6..6bf0a24 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -156,6 +156,7 @@ alloc_transaction:
 	 */
 repeat:
 	read_lock(&journal->j_state_lock);
+	BUG_ON(journal->j_flags & JBD2_UNMOUNT);
 	if (is_journal_aborted(journal) ||
 	    (journal->j_errno != 0 && !(journal->j_flags & JBD2_ACK_ERR))) {
 		read_unlock(&journal->j_state_lock);
-- 
1.7.1

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