jfs: fix a couple races

This patch fixes races uncovered by xfstests testcase 068.

One race is the result of jfs_sync() trying to write a sync point to the
journal after it has been frozen (or possibly in the process). Since
freezing sync's the journal, there is no need to write a sync point so
we simply want to return.

The second involves jfs_write_inode() being called on a deleted inode.
It calls jfs_flush_journal which is held up by the jfs_commit thread
doing the final iput on the same deleted inode, which itself is
waiting for the I_SYNC flag to be cleared. jfs_write_inode need not
do anything when i_nlink is zero, which is the easy fix.
Reported-by: Michael L. Semon <mlsemon35@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>

fs/jfs/inode.c

@@ -125,7 +125,7 @@ int jfs_write_inode(struct inode *inode, struct writeback_control *wbc)
 {
 	int wait = wbc->sync_mode == WB_SYNC_ALL;
 
-	if (test_cflag(COMMIT_Nolink, inode))
+	if (inode->i_nlink == 0)
 		return 0;
 	/*
 	 * If COMMIT_DIRTY is not set, the inode isn't really dirty.

fs/jfs/jfs_logmgr.c

@@ -1058,7 +1058,8 @@ static int lmLogSync(struct jfs_log * log, int hard_sync)
  */
 void jfs_syncpt(struct jfs_log *log, int hard_sync)
 {	LOG_LOCK(log);
-	lmLogSync(log, hard_sync);
+	if (!test_bit(log_QUIESCE, &log->flag))
+		lmLogSync(log, hard_sync);
 	LOG_UNLOCK(log);
 }