[PATCH v2] jbd2: Fix data missing when reusing bh which is ready to be checkpointed

[Zhihao Cheng]

Following process will make data lost and could lead to a filesystem
corrupted problem:

1. jh(bh) is inserted into T1->t_checkpoint_list, bh is dirty, and
   jh->b_transaction = NULL
2. T1 is added into journal->j_checkpoint_transactions.
3. Get bh prepare to write while doing checkpoing:
           PA				    PB
   do_get_write_access             jbd2_log_do_checkpoint
    spin_lock(&jh->b_state_lock)
     if (buffer_dirty(bh))
      clear_buffer_dirty(bh)   // clear buffer dirty
       set_buffer_jbddirty(bh)
				    transaction =
				    journal->j_checkpoint_transactions
				    jh = transaction->t_checkpoint_list
				    if (!buffer_dirty(bh))
		                      __jbd2_journal_remove_checkpoint(jh)
				      // bh won't be flushed
		                    jbd2_cleanup_journal_tail
    __jbd2_journal_file_buffer(jh, transaction, BJ_Reserved)
4. Aborting journal/Power-cut before writing latest bh on journal area.

In this way we get a corrupted filesystem with bh's data lost.

Fix it by moving the clearing of buffer_dirty bit just before the call
to __jbd2_journal_file_buffer(), both bit clearing and jh->b_transaction
assignment are under journal->j_list_lock locked, so that
jbd2_log_do_checkpoint() will wait until jh's new transaction fininshed
even bh is currently not dirty. And journal_shrink_one_cp_list() won't
remove jh from checkpoint list if the buffer head is reused in
do_get_write_access().

Cc: <stable@xxxxxxxxxx>
Signed-off-by: Zhihao Cheng <chengzhihao1@xxxxxxxxxx>
Signed-off-by: zhanchengbin <zhanchengbin1@xxxxxxxxxx>
Suggested-by: Jan Kara <jack@xxxxxxx>
---
 v1->v2: Adopt Jan's suggestion, move the clearing of buffer_dirty bit
	 and __jbd2_journal_file_buffer() inside journal->j_list_lock
	 locking area.
 fs/jbd2/transaction.c | 51 ++++++++++++++++++++++++++++---------------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 6a404ac1c178..06a5e7961ef2 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1010,36 +1010,37 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
 	 * ie. locked but not dirty) or tune2fs (which may actually have
 	 * the buffer dirtied, ugh.)  */
 
-	if (buffer_dirty(bh)) {
+	if (buffer_dirty(bh) && jh->b_transaction) {
 		/*
 		 * First question: is this buffer already part of the current
 		 * transaction or the existing committing transaction?
 		 */
-		if (jh->b_transaction) {
-			J_ASSERT_JH(jh,
-				jh->b_transaction == transaction ||
-				jh->b_transaction ==
-					journal->j_committing_transaction);
-			if (jh->b_next_transaction)
-				J_ASSERT_JH(jh, jh->b_next_transaction ==
-							transaction);
-			warn_dirty_buffer(bh);
-		}
+		J_ASSERT_JH(jh, jh->b_transaction == transaction ||
+			jh->b_transaction == journal->j_committing_transaction);
+		if (jh->b_next_transaction)
+			J_ASSERT_JH(jh, jh->b_next_transaction == transaction);
+		warn_dirty_buffer(bh);
 		/*
-		 * In any case we need to clean the dirty flag and we must
-		 * do it under the buffer lock to be sure we don't race
-		 * with running write-out.
+		 * We need to clean the dirty flag and we must do it under the
+		 * buffer lock to be sure we don't race with running write-out.
 		 */
 		JBUFFER_TRACE(jh, "Journalling dirty buffer");
 		clear_buffer_dirty(bh);
+		/*
+		 * Setting jbddirty after clearing buffer dirty is necessary.
+		 * Function jbd2_journal_restart() could keep buffer on
+		 * BJ_Reserved list until the transaction committing, then the
+		 * buffer won't be dirtied by jbd2_journal_refile_buffer()
+		 * after committing, the buffer couldn't fall on disk even
+		 * last checkpoint finished, which may corrupt filesystem.
+		 */
 		set_buffer_jbddirty(bh);
 	}
 
-	unlock_buffer(bh);
-
 	error = -EROFS;
 	if (is_handle_aborted(handle)) {
 		spin_unlock(&jh->b_state_lock);
+		unlock_buffer(bh);
 		goto out;
 	}
 	error = 0;
@@ -1049,8 +1050,10 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
 	 * b_next_transaction points to it
 	 */
 	if (jh->b_transaction == transaction ||
-	    jh->b_next_transaction == transaction)
+	    jh->b_next_transaction == transaction) {
+		unlock_buffer(bh);
 		goto done;
+	}
 
 	/*
 	 * this is the first time this transaction is touching this buffer,
@@ -1074,10 +1077,24 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
 		 */
 		smp_wmb();
 		spin_lock(&journal->j_list_lock);
+		if (test_clear_buffer_dirty(bh)) {
+			/*
+			 * Execute buffer dirty clearing and jh->b_transaction
+			 * assignment under journal->j_list_lock locked to
+			 * prevent bh being removed from checkpoint list if
+			 * the buffer is in an intermediate state (not dirty
+			 * and jh->b_transaction is NULL).
+			 */
+			JBUFFER_TRACE(jh, "Journalling dirty buffer");
+			set_buffer_jbddirty(bh);
+		}
 		__jbd2_journal_file_buffer(jh, transaction, BJ_Reserved);
 		spin_unlock(&journal->j_list_lock);
+		unlock_buffer(bh);
 		goto done;
 	}
+	unlock_buffer(bh);
+
 	/*
 	 * If there is already a copy-out version of this buffer, then we don't
 	 * need to make another one
-- 
2.31.1