jbd: use a single printk for jbd_debug()

Backport of jbd2 commit 169f1a2a87aae44034da4b9f81be1683d33de6d0
("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>

2 files changed, 24 insertions, 9 deletions

diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index 6510d6355729..2d04f9afafd7 100644
--- a/fs/jbd/journal.c
+++ b/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
  */
diff --git a/include/linux/jbd.h b/include/linux/jbd.h
index bc3e57d367fc..31229e0be90b 100644
--- a/include/linux/jbd.h
+++ b/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)