jbd: use a single printk for jbd_debug()

Backport of jbd2 commit 169f1a2a
("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.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/jbd/journal.c

@@ -90,6 +90,24 @@ static int journal_convert_superblock_v1(journal_t *, journal_superblock_t *);
 static void __journal_abort_soft (journal_t *journal, int errno);
 static const char *journal_dev_name(journal_t *journal, char *buffer);
 
+#ifdef CONFIG_JBD_DEBUG
+void __jbd_debug(int level, const char *file, const char *func,
+		 unsigned int line, const char *fmt, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	if (level > 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(__jbd_debug);
+#endif
+
 /*
  * Helper function used to manage commit timeouts
  */

include/linux/jbd.h

@@ -57,16 +57,13 @@
 #define JBD_EXPENSIVE_CHECKING
 extern u8 journal_enable_debug;
 
-#define jbd_debug(n, f, a...)						\
-	do {								\
-		if ((n) <= journal_enable_debug) {			\
-			printk (KERN_DEBUG "(%s, %d): %s: ",		\
-				__FILE__, __LINE__, __func__);	\
-			printk (f, ## a);				\
-		}							\
-	} while (0)
+void __jbd_debug(int level, const char *file, const char *func,
+		 unsigned int line, const char *fmt, ...);
+
+#define jbd_debug(n, fmt, a...) \
+	__jbd_debug((n), __FILE__, __func__, __LINE__, (fmt), ##a)
 #else
-#define jbd_debug(f, a...)	/**/
+#define jbd_debug(n, fmt, a...)    /**/
 #endif
 
 static inline void *jbd_alloc(size_t size, gfp_t flags)