jbd2: use a single printk for jbd_debug()

Since the jbd_debug() is implemented with two separate printk()
calls, it can lead to corrupted and misleading debug output like
the following (see lines marked with "*"):

[  290.339362] (fs/jbd2/journal.c, 203): kjournald2: kjournald2 wakes
[  290.339365] (fs/jbd2/journal.c, 155): kjournald2: commit_sequence=42103, commit_request=42104
[  290.339369] (fs/jbd2/journal.c, 158): kjournald2: OK, requests differ
[* 290.339376] (fs/jbd2/journal.c, 648): jbd2_log_wait_commit:
[* 290.339379] (fs/jbd2/commit.c, 370): jbd2_journal_commit_transaction: JBD2: want 42104, j_commit_sequence=42103
[* 290.339382] JBD2: starting commit of transaction 42104
[  290.339410] (fs/jbd2/revoke.c, 566): jbd2_journal_write_revoke_records: Wrote 0 revoke records
[  290.376555] (fs/jbd2/commit.c, 1088): jbd2_journal_commit_transaction: JBD2: commit 42104 complete, head 42079

i.e. the debug output from log_wait_commit and journal_commit_transaction
have become interleaved.  The output should have been:

(fs/jbd2/journal.c, 648): jbd2_log_wait_commit: JBD2: want 42104, j_commit_sequence=42103
(fs/jbd2/commit.c, 370): jbd2_journal_commit_transaction: JBD2: starting commit of transaction 42104

It is expected that this is not easy to replicate -- I was only able
to cause it on preempt-rt kernels, and even then only under heavy
I/O load.
Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Suggested-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/jbd2/journal.c

@@ -103,6 +103,24 @@ EXPORT_SYMBOL(jbd2_inode_cache);
 static void __journal_abort_soft (journal_t *journal, int errno);
 static int jbd2_journal_create_slab(size_t slab_size);
 
+#ifdef CONFIG_JBD2_DEBUG
+void __jbd2_debug(int level, const char *file, const char *func,
+		  unsigned int line, const char *fmt, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	if (level > jbd2_journal_enable_debug)
+		return;
+	va_start(args, fmt);
+	vaf.fmt = fmt;
+	vaf.va = &args;
+	printk(KERN_DEBUG "%s: (%s, %u): %pV\n", file, func, line, &vaf);
+	va_end(args);
+}
+EXPORT_SYMBOL(__jbd2_debug);
+#endif
+
 /* Checksumming functions */
 int jbd2_verify_csum_type(journal_t *j, journal_superblock_t *sb)
 {

include/linux/jbd2.h

@@ -56,17 +56,13 @@
  */
 #define JBD2_EXPENSIVE_CHECKING
 extern ushort jbd2_journal_enable_debug;
+void __jbd2_debug(int level, const char *file, const char *func,
+		  unsigned int line, const char *fmt, ...);
 
-#define jbd_debug(n, f, a...)						\
-	do {								\
-		if ((n) <= jbd2_journal_enable_debug) {			\
-			printk (KERN_DEBUG "(%s, %d): %s: ",		\
-				__FILE__, __LINE__, __func__);	\
-			printk (f, ## a);				\
-		}							\
-	} while (0)
+#define jbd_debug(n, fmt, a...) \
+	__jbd2_debug((n), __FILE__, __func__, __LINE__, (fmt), ##a)
 #else
-#define jbd_debug(f, a...)	/**/
+#define jbd_debug(n, fmt, a...)    /**/
 #endif
 
 extern void *jbd2_alloc(size_t size, gfp_t flags);