[PATCH 4/4] jbd: use a single printk for jbd_debug()

[Paul Gortmaker <paul.gortmaker@windriver.com>]

Backport of jbd2 commit 169f1a2a87aae44034da4b9f81be1683d33de6d0
("jbd2: use a single printk for jbd_debug()")

Quoting the original:
 --------------
 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>
---
 fs/jbd/journal.c    | 18 ++++++++++++++++++
 include/linux/jbd.h | 15 ++++++---------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index 166263d..f45f0a3 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -97,6 +97,24 @@ 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 > jbd_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
  */
diff --git a/include/linux/jbd.h b/include/linux/jbd.h
index e45b430..d6d3ae0 100644
--- a/include/linux/jbd.h
+++ b/include/linux/jbd.h
@@ -56,16 +56,13 @@
 #define JBD_EXPENSIVE_CHECKING
 extern ushort 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)
-- 
1.8.1.2